Limestone's Lesson

by TheVClaw

Rating: mature
Tags: Limestone Pie, Non-consensual, Random, Cloudy Quartz, Pinkie Pie, Igneous Rock, Profanity, My Little Pony: Friendship is Magic, Dark, Marble Pie, Porn, Fetish
Length: 29017

Limestone's sisters were supposed to help her look over the rock farm while their parents were away. Unfortunately, after discovering Pinkie and Marble Pie napping on the job, Limestone decides to implement a rather... unorthodox punishment for them~

NOTE: This story is an ABDL commission for PokemonVictor, and will contain diaper-related fetish content. If you're not cool with that, don't bother reading this. There will also be themes which include desperation, humiliation, semi-incestuous scenes and bondage. Reader Discretion is obviously advised.

Limestone may have been one of the hardest workers on her family's rock farm, but even she knew the importance of teamwork and sharing the load when it came to finishing tasks. She usually worked alongside her sisters Marble Pie and Maud, as well as her parents; however, after Maud moved away for college, and her parents were called away for an emergency meeting, Limestone hoped that Pinkie Pie's visit would help make up for the overbearing workload.

Unfortunately for Limestone, she was nearly finished with her grueling work when she discovered both of her sisters had slipped away from their chores. And when she found Pinkie and Marble taking a nap in the middle of the day, the exhausted mare was absolutely livid.

So what does she do? Normally she would've yanked them out of bed and scare them half to death. But after recent circumstances that landed her in court-mandated therapy, Limestone had a peculiar idea -- albeit an extreme one -- guaranteed to teach her sisters the importance of being an adult...

... by having them be babies for the rest of the day~

Published 2022-03-17 19:30:02 UTC
Last updated 2022-03-25 00:32:58 UTC

Chapter One

“Nnnnnfffff!! Grrrrrghhhhh…”

A pair of dirtied, light gray hooves were constantly skidding across the dusty ground, leaving several thin divots wherever her weight beared down the most. The bottom of the worn-down keratin, as well as the bushy fetlocks that went up those muscular legs, were covered with a deep shade of brown to match all the dirt being kicked around. The trail of skids and divots went off quite a ways in the distance, indicating that the hard work was certainly showing a positive effect. But alas, by the time those last few strenuous groans were given from the mare in question, her successful efforts amounted to merely moving a carriage-sized boulder across the rocky field.

“Whew!~” The young mare breathed a deep sigh of relief, and finally dropped her hooves to slump against the side of the gargantuan boulder. Her purplish gray coat was matted in sweat, which meant that most of the dust she kicked around was sticking to it and making her look even dirtier. Her cutiemark of a lime-wedge and two rocks were partially hidden beneath all that dust, not that she seemed to mind after so much work. Her long, straight silver mane was clinging to her head and the back of her neck, while her face had several dirty smears where she had to continuously wipe her fur. She took several deep, panting breaths after such an intense session, which would’ve usually taken her and half the family to complete safely. Unfortunately, outside circumstances meant that Limestone was forced to do the brunt of the work on her own that weekend.

“Haaaa… Haaaaahhhhh…” Limestone hung her head, which made her sweaty mane cover her face and put it under a makeshift shade from the blistering sun above. Ever since her sister Maud left for college earlier in the Spring, she and the rest of the family had to pick up her share of the work; granted, she was certainly proud of Maud getting an education, but she still wished her parents hired some helping hooves. Even on that particular weekend, when the two had to make an emergency trip to Baltimare for a cousin’s intervention (again, something that Limestone couldn’t blame them for doing), she had to bite her lip to keep from cursing at their stinginess. Instead of asking for help from neighbors, or just paying some high schoolers to come by and learn the intricacies of rock-farming, Limestone could only shake her head and mutter to herself, “Jeeze… W-Where the heck is Pinkie at?”

She finally looked up while leaning against the boulder, and her eyes widened when she realized how silent and desolate the farm was. While that certainly wasn’t something worth complaining about, she didn’t realize how long it had been since she last heard her sister’s cheery voice. Pinkie Pie had only arrived the previous night, but Limestone remembered her distinctly saying she would help “as hard as she could” alongside herself and their sister Marble. But instead of hearing her bubbly laughter, or a plethora of impromptu songs to fill the monotonous void all around, Limestone’s ears perked up before growing a bitter sneer on her muzzle.

“Nnnnghhh…” Limestone regained more than enough energy to not only pull away from the boulder, but to hop on top of it so she could better scan her surroundings. The Pie Family’s rock farm went out for dozens of acres all around; but at the same time, it was all flat and bare enough for Limestone to see the farm’s borders without many hiding spots. It only took the mare a few minutes to stare around the entirety of the farm grounds, only to be met with nothing but the sight of rocks all around. If it was just her sister Marble, Limestone would’ve just assumed that she was hidden somewhere among the thicker regions of rocks similar to her gray coat. But when she wasn’t able to see a speck of pink anywhere on the premises, Limestone quickly got agitated.

“Grrrrr!!! WHERE ARE THEY?!” Limestone stood up on her hind-legs atop the massive boulder, and she shouted out loudly enough to make her voice echo all around. “PINKIIIIEEEEE!!! MARBLLLLLEEEE!!! WHERE ARE YOU TWO?!”

Limestone expected to hear some galloping hooves, or maybe even a scared shriek from Marble in response to her booming voice. But alas, as the seconds of deafening silence passed, the mare’s teeth gritted tightly to reveal a more angered expression. She eventually hopped off the huge rock, and stormed over towards the opposite end of the fields where her sisters were supposed to be at. She muttered under her breath, “I swear, if those two tried to leave me with all the morning tasks before lunchtime…”

In a span of ten minutes, Limestone’s anger went from slightly miffed to absolutely furious. As soon as she reached the eastern fields, where Marble Pie was supposed to be, she was met with only a half-finished pile of sedimentary stones that should’ve taken an hour to complete. Marble may have not been nearly as productive as herself, but Limestone couldn’t fathom how she managed to screw up a task so simple. And when she ventured over towards the southern end of the fields, where Pinkie Pie was usually the best at tending to in her earlier years, Limestone was appalled to see that her rock pile was only a quarter of the way finished.

“Oh, for CRYING OUT LOUD!!!” Limestone stormed back towards the Pie Family farmhouse, her dirtied face as red as a sunburnt beet. She may have known the three of them had a hefty workload to handle for a single weekend; but with the number of geologists and rock specialists the family has to work with, who all require strict deadlines and harsh penalties for late deposits, the last thing she needed was to deal with those headaches due to other ponies’ faults. Part of her wanted to crash into the house at full-force, and raise total Tartarus against her sisters for slacking on the job. But just as she was about to reach her home’s front porch, the mare paused briefly enough to close her eyes and take a couple breaths.

“Wait a minute, Limestone,” she muttered to herself in an attempt to keep from snapping. “Think about what Doctor Elderberry taught you… Breathe in… Breathe out…”

Limestone spent a good minute practicing her breathing techniques, which helped significantly to decrease her anger and keep her from doing anything drastic. Doctor Elderberry may have been a court-appointed therapist, but she couldn’t deny how helpful his advice may have been since that grocery store incident. If it wasn’t for that crotchety old stallion, Limestone would’ve likely put her family under even more financial heartache from that potential assault lawsuit. And even with some of the doctor’s more… unique therapy techniques, which led to some unusual methods of relaxation on Limestone’s end, she wasn’t one to ignore his methods when they showed so much progress already.

After a brief moment of much-needed reprieve, Limestone didn’t feel nearly as violent when she let out a calming sigh. In fact, the mare was able to keep herself quiet when she entered the farmhouse all dirty and sweaty. She took her time as she trotted through the modest home, which laid completely still like the rock fields outside. Part of her was trying to justify her own silence as a logical response to her breathing techniques, and not just as a means to catch her sisters with whatever they were doing aside from work. But even with her muzzle shut, it clenched tightly the moment she saw a distinct mess in the kitchen.

All across the kitchen counter, several bottles of fresh farm-made milk were strewn about and emptied from their distinct glass containers. Limestone’s left eye twitched when she saw how many there were, which she could only assume were purchased by Pinkie earlier in the morning from the dairy farm next door. Sure, it would’ve been easy to assume that Marble bought so much fresh milk, or even her parents before went off to Baltimare; however, Limestone could see clear as day that several of the bottles had brown and pink tints on the inside of the glass, which indicated that they were flavored with sugary syrups.

“Nnnnnghhhh!!!~” Limestone bit down hard on her hoof, nearly drawing blood. Fortunately for the mare, that was the only outburst she gave at seeing the aftermath of Pinkie Pie’s milk binge. She had no idea how the fresh milk in Ponyville compared, but she could only assume it wasn’t the same quality as it was around this region. Nevertheless, that was no excuse for the mare to drown herself with dairy when so much work had to be done. Limestone dragged her hoof down her face in frustration, but she managed to keep herself from blowing up and giving her sisters a chance to hide. By the time she took a couple more breaths, she was calm enough to go up the stairs and see if they were on the second floor.

Limestone didn’t need to look far to discover where Pinkie and Marble were hiding. Of course, she couldn’t say that neither of them were “hiding” in the slightest. As soon as she peered into the open doorway of their shared bedroom, her muzzle dropped when she saw Pinkie and Marble sprawled out on the bed and completely asleep. Pinkie Pie was snoring louder than a tugboat’s engine, with the outside of her muzzle matted with a thick coat of lingering milk that made her breaths reek of chocolate and strawberry. Marble Pie, who usually had a stronger worth ethic compared to her twin sister, appeared equally as comatose with a small milk mustache of her own. Both of them were nestled together on the bed, since apparently a little “nap” seemed more appealing than actually getting work done. Limestone didn’t say anything at that moment; although, that was most likely because she was too enraged to speak through her gritted teeth.

Her agitated groan was nearly silent, and her face grew red enough to nearly singe the hairs of her fur from how enflamed her rage was getting. It took every fiber of her being not to yank those two lazy-bones off the bed, and drag them by their ears to the fields to get their work done. But just as she was about to lift a hoof, Limestone froze with her eyes widening in an instant. As a look of revelation grew across her face, Limestone recalled a specific quote that Doctor Elderberry recommended to her during one of their most recent sessions.

“Just remember, Miss Limestone… Before you think to act impulsively, I want you to think to yourself: ‘What would be the best means to solve a problem without violence?’”

Back when he first told her that, the mare assumed it was just a bunch of hogwash to keep her from getting another assault charge. But in that moment, with her two sisters still lying about in the middle of a deep sleep, Limestone blinked a couple times before growing a rather devious grin. She had no idea what came over her, but she no longer felt upset upon seeing Pinkie and Marble sleeping on the job. Instead, the mare went over towards the nearby desk, and grabbed the wooden chair before leaving the room silently.

She carefully closed the door, before propping the chair against the knob so it couldn’t open from the inside. After making sure the chair’s back-legs were secure, and the back of the chair was tightly nestled underneath the knob, Limestone trotted back downstairs so her sisters could get their “much-needed” rest. By the time she went back outside towards the fields, Limestone was able to estimate that she could get both of their work done in less than three hours time. Hopefully by then, both of them will come to terms with what was likely to happen next as punishment…

The sun was much closer to the horizon by the time Limestone returned to the farmhouse, her fur completely matted in a mixture of dust and sweat. Even though the shared tasks that Marble and Pinkie were supposed to do took a bit longer than expected, the mare felt rightfully content with her hard work. As soon as she entered through the front door, she huffed with a devious grin when she heard the muffled sounds of banging upstairs. But instead of tending to her sisters’ dire pleas, she went straight towards the downstairs bathroom to freshen herself up.

Upstairs, the sounds of Pinkie’s violent banging reverberated throughout the whole house. “LIMESTONE!!!” shrieked the pink mare desperately, “PLEASE LET US OUT!! WE’RE SORRY!!”

“We’re SO sorry!” cried out Marble’s voice, which was probably the loudest she ever yelled. Limestone could hear both of them clear as day, but that didn’t stop her from running a cold shower for herself. While the pipes could be heard running outside the bathroom, Pinkie still yelled like a banshee from upstairs.

“LIMESTONE, PLEASE!!! We’ve been in here for SO long!!!” A deep, desperate-sounding groan could be heard through the bedroom door. Pinkie and Marble may have tried their hardest to break out, but the chair didn’t budge an inch while wedged against the knob. And since the drop from the second floor was far too high for either of them to escape through the window (especially when a bunch of jagged rocks were positioned underneath the window outside), they were hopelessly trapped until Limestone finished her shower. “Urrrghhh… C-C’MON!! Limestone, I… I-I really need to go!!!”

When the hard-working mare finally finished her long, refreshing shower, she stepped out of the bathroom with a brisk smile while hearing the banging upstairs. She took her sweet time as she walked her way up the stairs, paying no heed to how dire or agitated Pinkie and Marble’s voices may have sounded. Instead, all that the mare did was walk over to the upstairs bathroom, and retrieve a small bag she had hidden underneath the sink. All the while, she was smirking to herself while hearing her sister’s cries for help upclose.

“LIMESTONE, I CAN HEAR YOU!!! LET US OUT RIGHT NOW!!!”
“P-P-PLEASE, Limestone! We’re sorry!”
“I CAN’T STAY IN HERE FOR MUCH LONGER!!!”
“N… N-Neither can I!”
“Okay, I’ll admit it! I drank too much milk! I’m SORRY!!! Is that what you want to hear!?!”
“I-I’m sorry too…”
“LET US BOTH OUT RIGHT NOW!!!”

“Hmph…” Limestone was still grinning to herself by the time she emerged from the bathroom with her bag over her shoulder, and a small metallic key hanging from a chain around her neck. She made sure that the bathroom door was closed tightly shut, before using the key to lock the knob from the outside. After testing how sturdy the lock was, she smiled in satisfaction before walking over to the bedroom. She was impressed with how well the chair held up, even against Pinkie and Marble’s combined strength. Regardless, she waited only a moment for the banging to stop before speaking up with a cheeky tone. “Well, well, wellllll… I’m guessing you and Marble had a nice little nap, huh?~”

There was a brief moment of silence from the other side of the door. Limestone waited patiently for a response, which came after Pinkie gave a long and accepting sigh. “Ughhhh… O-Okay, I… I’m really sorry, Limestone. I was just super, duper excited to have some local milk again, and I… I didn’t mean to pass out, alright?!”

“M… M-Me neither,” muttered Marble with an equally guilty tone.

Limestone tilted her head while staring at the door separating them. “Well, that doesn’t make up for the fact that I had to do ALL of your tasks today! By MYSELF! Are you aware how long I was out there on my own while you two slept the day away?”

“WE SAID WE’RE SORRY!!!” Pinkie banged on the door a few more times in frustration, not that it seemed to faze Limestone in the slightest. Instead, the mare stood with a smug smirk while waiting for any further response. “Nnnnnghhh!!! Okay, what do you want from us, Limestone?! We apologized and we feel really bad, what more do you need?!”

“P-Please!” squeaked Marble in addition. “I… I really… mnnnghhh…”

That half-finished statement made Limestone grin even wider, although she was grateful neither of her sisters could see that. “Oh, is that so? Well, let me ask you this… Do you know WHY I’m so upset?”

“YES, CLEARLY!!!” screamed Pinkie angrily. “You made your point!!”

“Oh, I don’t think I did…” Limestone got up closer to the door with her smirk lessening to an angry sneer. “You see, I was the ONLY pony today who cared enough about this farm to act like an ADULT!!! What do you think Mom and Dad would say?! Do you think they’d approve of you two sleeping around like a couple of babies?!”

Another awkward bout of silence came between them. Pinkie and Marble eventually relented with a shared tone of guilty voices. “... We’re sorry, Limestone…”

“Well, we’ll see about that~” Limestone unzipped her bag, and began to unload the items inside to lay outside the door. “Now, before I open this door to let you out, I need you to PROMISE you don’t back down from this punishment, alright?”

“WHAT?!” Pinkie sounded outright pissed by that point. “YOU ALREADY LOCKED US IN HERE!!!”

“Yes, but you two need to learn how to be adults! Maybe you’ll come to appreciate it after this~” Limestone had to keep from snickering to herself, but was able to stay silent as she laid out a large rubber mat. After making sure everything was in check, she stood outside the door and repeated her insistent claim. “Now… if you two agree to do this punishment, I’ll unlock the door and let you out. But if either of you refuse, you’ll stay in there without dinner! And you KNOW I’ll do that if necessary!”

Nearly a minute of uncomfortable silence lingered between the ponies on both sides of the door. Limestone waited patiently, and kept her confident smirk while staring at the knob. Pinkie and Marble Pie didn’t say anything for a while, but she was sure they were contemplating their options. After a long moment, Pinkie could be heard sighing through the door in a mixture of defeat and desperation. “Oh… O-Oh alright, ALRIGHT!!! If… If you let us out, we’ll do whatever you say!! Cross my heart, hope to fly, stick a cupcake in my eye!”

Limestone’s eyes widened in surprise, not expecting her sister to make such a serious pact to show her sincerity. It may have not been enough to avoid punishment, but she was especially glad Pinkie did it. She waited only a second or two before asking through the door, “Marble? Do you Pinkie Promise too?~”

Usually, she wouldn’t think to subject Marble to this kind of thing. But after all the grueling work she did outside, she was happy to hear her sister mutter through the door, “Ummmm… C-Cross my heart, hope to fly… s-stick a cupcake in my eye…”

“Okay, that’s good to hear…” Limestone finally went to pull the door away from the knob. “Now, as soon as I unlock this door, you’re going to do EXACTLY as I say. Do you two understand?~”

Despite how agitated Pinkie’s groan may have sounded, she was happy to hear her and Marble agree without hesitation.

“YES, WE’LL DO WHATEVER YOU SAY, JUST LET US OUT!!!”
“P-Please… Mnnnghhh…”

Limestone silently pulled the chair out of the way, which left the door completely unlocked. She then grabbed two items she had laying on the floor, and stood on her hind-legs with one in each hoof. “Alright, open up the door slowly…”

With that insistent detail, the knob slowly turned before finally opening up. Pinkie Pie and Marble Pie were already blushing deeply, clearly in need of certain functions that their bedroom couldn’t provide. Unfortunately for the two, they froze up the moment they stood at the doorway and saw what their sister was holding. Limestone grinned even wider, and made sure both of them could see the plushy white rectangles held in both hooves. Marble Pie blushed even deeper, with her eyes growing as wide as saucers. Meanwhile, Pinkie’s pupils shrunk quite a bit before she tried to ask worriedly:

“Uhhhh… are… are those diapers?”

“Yes they are~” Limestone motioned down to the changing mat she laid out on the floor, right beside her fully-loaded diaper bag. The items may have been for her own personal use; but in that moment, her focus was entirely on her two lazy sisters as she grinned like a madpony.

“And since you two want to doze around like a couple of babies, I’m gonna make sure you act like them too~”

Author's Note

Just in case anyone was curious, the entire five chapter story (as well as an extra bonus chapter) are already up on my Official Patreon Page.
I also wanna give a big thanks to PokemonVictor for commissioning this story, which helped pay multiple bills while my boyfriend and I prepare to move cross-country. If any of you want to help with our upcoming travel plans, I'm accepting any and all donations via Paypal

Chapter Two

“WHAT?!?”

Pinkie Pie and Marble Pie stood with equally shocked looks on their faces. Their eyes and muzzles were wide-open as they pointed right at their sister’s smug grin. Limestone didn’t seem to show any embarrassment or worry as she stood before the two on her hind-legs; of course, that was most likely because she knew she wasn’t the one about to wear the poofy pieces of padding in her hooves.

“You heard me,” she said with utmost confidence. Even as her sisters’ stunned expressions began to blush profusely, she remained diligent as she motioned towards the changing pad. “You left ME to do all the work outside, so it’s only fair you two face the consequences.”

Pinkie’s eyes repeatedly darted between her sister’s imposing stance, and the bathroom door only a few feet away. “Uhhh, w-wait a minute!” Before Limestone could get the chance to stop her, the pink mare rushed towards the door with her fur standing on end. But alas, as soon as she grabbed the knob with both hooves, Pinkie gasped in a panic when she realized it was locked. She tried yanking back on the knob several times to no avail, which caused her hind-legs to bunch together and tremble upright.

“Mmmphhhh…” Marble Pie blushed even deeper, and tried to bite her lip in an attempt to quell her own building feelings of pressure. But much like her sister, who was squirming badly and desperate to unlock the bathroom door, Marble whimpered and tried her best to keep her legs clenched inward. Limestone just smirked while standing in wait, admiring how badly the two were struggling already. And since she was standing between her sisters and the stairs, she wanted to make sure they didn’t try to leave unprepared.

“I also locked the downstairs bathroom as well.”

Pinkie and Marble gawked back at their sister, but neither of them could say much in response to her unchanged grin. “So unless the two of you want to have a little accident, I recommend you get these on pronto~”

“W-W-WAIT A MINUTE!” Pinkie turned around to face Limestone with a shocked and upset glare. “L-Limestone, come on! This isn’t funny!”

“I didn’t say it was funny,” she replied with a lighthearted shrug. “Do I look like I’m laughing?~”

“Nnnnnghhh…” Marble Pie’s head hung down as she groaned to herself needily. Her hind-legs pressed in even tighter together, leaving her quivering in an obviously dire state. Pinkie could only take seeing her sister’s squirming for a second before looking away, since her own building pressure was causing her hooves to shuffle against the hardwood floor. Neither of them wanted to admit what they needed to do, but they could tell that Limestone knew clear as day already. Unfortunately, the idea of complying with her method of “punishment” felt far worse than just holding it in for the time being.

“P… P-Please, Limestone…” Marble had to lean up against the wall while trembling like a fallen leaf. Her knees were wobbling badly, and her tail was tightly tucked between her tensed legs. “I… Idon’twannadothat…”

“Well, I didn’t want to pick up both of your chores. Especially because of a little milk-binge.” Limestone stared daggers back at Marble, her expression more disappointed than anything. “Honestly, I would’ve expected that from Pinkie, but not you.”

Even with her body twitching badly, Marble Pie could only hang her head in shame. Pinkie Pie groaned more angrily, and tried to storm up towards their sister. “Okay, SERIOUSLY, Limestone?! I know you’re upset, but that doesn’t mean you have to punish BOTH of u--OOFFF!!!”

Before she could finish her ranting, or even get the chance to apologize to Limestone face-to-face, Pinkie Pie was picked up with disturbing ease by her sister. Limestone effectively got the pink mare thrown onto her back, right on top of the changing mat. Pinkie groaned and struggled against her sister’s grip, but the seasoned rock-farmer had considerable strength against the pastry baker. Pinkie yelped out the moment Limestone used one of her rear hooves to nestle between her legs, spreading them apart and making the pressure in her bladder more immense.

“Aaahhhh!!~” Pinkie’s back reeled up from the changing mat, and her blush grew heavier from the growing pressure she was feeling. Limestone used one of her hooves to hold Pinkie’s forelegs over her head, which kept her from trying to pull herself up. She used her other hoof to press down ever-so-slightly against the bottom of Pinkie’s stomach. Due to how much milk she drank several hours ago, only the tiniest bit of pressure was needed to make her tense up against Limestone’s grasp. Her hind-legs squirmed and fidgeted like mad, but the hooves merely skidded against the hardwood floor without any grip. And all the while, Marble Pie just stared with fearful awe at how effectively Pinkie Pie was subdued. “P-P-Please, Limestone! Don’t… D-Don’t push me there!!!”

“Oh, really now?” Limestone smirked more devilishly, and she kept her hoof faintly pressed against the pink mare’s stomach. Pinkie clenched her eyes shut and let out a strained groan, while her hind-legs crossed tightly together to keep herself stable. Limestone kept the pressure unchanged for a few more seconds, and waited until Pinkie stopped grunting to speak firmly. “Now then… do you want to keep fighting me, or are you going to take your punishment like a big girl?~”

“Nnnnnghhh…” Pinkie Pie glared up at her sister with a pained scowl, and had to take a couple breaths through her nostrils. Marble Pie tried to subtly move towards the bathroom door, but much like her sister, she was thwarted by the knob remaining tightly locked. She lurched down for a moment with another heated sigh, and stared back at the other two to see what happened next. Pinkie eventually closed her eyes so she could breath out calmly, and finally relented with a small nod. “... f… f-fine…”

“That’s what I thought~” Limestone finally let go of Pinkie’s stomach, as well as her forelegs before positioning herself between her sister’s legs. She used her immense strength to easily grab both of Pinkie’s ankles in one hoof, causing her to groan out and writhe against her grip. Marble watched in stunned silence as her sister got Pinkie’s backside lifted up from the mat with one hoof, while the other unfolded one of those diapers to lay underneath her. As soon as Pinkie’s rump was lowered onto the plush white padding, Limestone pried apart her legs so she could fold the front of the garment over her nethers.

“Nnnnnnghhhh…” Pinkie couldn’t even look down at herself, and covered her face with both hooves in embarrassment. She was blushing heavily with dread as Limestone got the padding securely wrapped around her waist, with the tapes applied to the sides without any issue. As soon as Pinkie was fully diapered, Limestone turned to face Marble with a firm stare.

“You’re wearing a diaper too,” she commanded with a stern voice, and a slightly vindictive smile across her muzzle. “And until both of you use them in front of me, they’re not coming off~”

“WHAT?!?”

Once again, Pinkie and Marble stared up at Limestone like she just said the most insane thing imaginable. Pinkie may have already been padded up, but she gawked at her sister’s “punishment” in shock and disgust. “Y-You want us to… t-to USE them?!”

Marble’s head lowered in an attempt to hide her paled expression, but she still tried to mutter out, “You… Y-You mean, like…”

Limestone didn’t wait for her to finish that clarification, and merely nodded at both of them smugly. “Well, what do you expect to do in diapers? If you two don’t want to take responsibilities like adults, I don’t expect you to go to the bathroom like adults either~”

Before Pinkie could get the chance to pull herself off the mat, Limestone reached into her bag to pull out a secondary item of protection for both of them: a pair of see-through, plastic shorts with elastic cuffs. “And just in case there’s any leaks, I expect these to be put on as well~”

Limestone began to slide the plastic pants up Pinkie’s squirming legs, while the mare herself whimpered with a worried grimace. While Pinkie was given that second later of foalish protection, Marble reached down to pick up the unused diaper laying beside her sisters. She blushed upon feeling how soft and poofy the plastic was against her hoof. “Oh my gosh… Wh… W-Where did you get these from?”

“They weren’t cheap, I can tell you that.” After rolling Pinkie Pie over for a split-second, which resulted in a loud click to get the pants secure, Limestone helped her sister up so she was back on her hooves. “Seriously, you would not believe how expensive adult diapers can get. Unless you get the cheap medical brands that barely work, each of these pairs cost like, five bits apiece!”

Pinkie’s muzzle was quivering when she finally stood back upright, her hind-legs notably spread a bit wider while so much plastic padding was bunched between them. The diaper was bright white beneath the pants’ transparent plastic, and thick enough to make it impossible for her to walk normally. Marble’s fearful look intensified when she saw the end result of Pinkie’s padding, knowing that she was next in line. “Wh… Why do you have them?”

Marble’s question prompted Limestone to glance back at her, while she and Pinkie just stared back in wait for a response. Limestone didn’t seem too embarrassed to admit with a shrug, “Well, let’s just say that Doctor Elderberry’s ‘Regressive Relaxation Therapy’ has worked wonders in keeping my anger in control.”

“Nnnnfffff…” Pinkie glared at her with a withheld groan, looking like she was about to blow up at her for such a claim. But considering what she was wearing around her waist, not to mention how badly her bladder was swelling inside of her, she was barely able to keep her composure in check to even speak.

“Now, come on!” Limestone pointed to the mat authoritatively, and stared Marble down with an annoyed grimace. “I don’t want to throw YOU onto the mat too! Just get it on so we can get this punishment over with.”

“NNNGHHHH!!!” Pinkie shouted out angrily, “Limestone, I am NOT going to use this diaper!”

“Hmph~ Well, we’ll just see about that…” Limestone paid no heed to her sister’s pissed-off sneer, and watched with a satisfied smile as Marble timidly walked towards the mat. Unlike Pinkie, who could barely stand in her diaper while her knees were wobbling, Marble Pie shivered with a blush and willingly laid on her back atop the mat. She didn’t give any resistance when her sister got between her legs, and lifted her up by her ankles. However, Marble still groaned weakly when she felt the unfolded diaper being laid underneath her rump, before Limestone lowered her back down and got the padding securely wrapped in place.

“Just a few tapes here and there, and… perfect!” Limestone grinned in satisfaction by the time Marble was diapered like their sister. She then got the second pair of plastic pants out of her bag, and began to slide them up Marble’s legs. “And if it means anything, I promise I’ll get you two cleaned up after you do it~”

Limestone gave a cheeky wink after that promise, which made both of her sisters wince uncomfortably. While the pants were being secured in place, Marble waited until she was rolled onto her stomach to ask, “W-Wait, do… do you seriously wear these for therapy?!”

Given how wide-eyed Pinkie was staring at Limestone, it seemed that she was wondering the exact same thing as Marble. Once again, Limestone just shrugged indifferently after securing the pants in place with another click. “Well, it works… I won’t try to lie and say it’s for everypony, but I’m not one to deny its results~”

She helped Marble back onto her hooves, with her hind-legs also spread apart with all the white plastic bunched against her nethers. Marble and Pinkie were left standing side-by-side, with their blushes as notable as the thick padding wrapped around their backsides. Limestone took a moment to grin at the two smugly, happy to give her sisters a well-deserved taste of humble-pie. However, she was also quick to sigh before adding assuredly, “And yes, I know exactly how those feel on you right now. Trust me, I wouldn’t give you two a punishment I hadn’t experienced myself~”

That remark caused Pinkie and Marble to stare at each other worriedly. Neither of them were sure what all Limestone had done in diapers herself, but they certainly didn’t want to ask either. Instead, all they could do was look back at the poofy garments hugging both of their rumps so tightly. Pinkie was the first to try and move one of her legs, and shuddered when she heard the loud crinkling of the plastic and padding against her crotch. Marble could barely move, but she could hear the faint crinkling from her own diaper when she shivered a little.

“Alright, let’s get you babies downstairs!” Limestone led the way as she trotted past the two padded mares, and went down to the first floor. “I already have a little ‘lunch’ set up for the both of you. Heh heh~”

Pinkie and Marble winced at how cheekily Limestone said that. As soon as she was out of sight, Pinkie got in close to whisper into her sister’s ear, “Okay, no matter what happens, we can NOT give her the satisfaction. Whatever you do, just… just keep it in, okay?!”

“Kee… Keep it in?!” Marble’s eyes darted around whie whimpering under her breath. “Nnnffff… I… I don’t think I can do it, Pinkie…”

“You rather want her to watch you wet yourself?!” That idea made both of them shudder uncomfortably. Pinkie seemed especially unnerved as she shook her head. “No. W-We can’t let that happen! Let’s just try our best to… I dunno… w-wait it out or something…”

Marble sighed and nodded in agreement to Pinkie’s plan. Unfortunately, as the two tried their best to slowly waddle down the stairs, each stretch of their legs reminded both of them of how badly they needed to go. The last thing either of them wanted to do was endure such a humiliating punishment under Limestone’s orders; but alas, neither of them were sure how long their resistance could last…

“Oh, girrrrrllllssss… Come on doooowwwwnnn~”

Pinkie and Marble were groaning badly by the time they reached the bottom of the stairs. They weren’t sure which was more discomforting: the growing pressure both of them felt in their bladders, or the obviously vindictive tone in Limestone’s sing-song voice. This may have been a “punishment” for the two of them, but it was clear that their sister was enjoying it just a little too much. If their parents were still here, they would’ve waddled right over to them in an attempt to stop Limestone’s debauchery from going any further; but alas, the two diapered mares were left alone to face her incoming wrath.

They were blushing hard when they finally waddled their way into the kitchen, with their diapers loudly crinkling with every step to alert Limestone of their presence. The mare was already standing with a cocky grin, while an old high-chair was pulled out of storage to serve as the girls’ new seating. Marble Pie blushed worriedly at seeing the vintage chair already placed at the table. Meanwhile, Pinkie Pie just stared at Limestone flatly. “... seriously?”

“Seriously~” Limestone gave the chair a playful pat with her hoof while staring the two down. “Apparently, Mom and Dad gave the other high-chairs to the neighbors after their grandchildren were born. But since we still have this one, I’ll let you decide who gets a seat first~”

Pinkie and Marble stared back at one another with matching looks of silent dread. Marble softly shook her head, not wanting to try and sit in that tiny seat while her rump was so thickly padded. Pinkie didn’t appear to be too thrilled about the concept either; however, the last thing she wanted to do was subject her sister to a fate caused by her own actions. Since she was the one to get both of them napping in the first place, Pinkie closed her eyes with a sigh before turning back to Limestone. “Ughhhh… I… I guess I’ll do it…”

“Perfect!” Limestone grinned devilishly while lifting up the serving tray latched above the seat. Pinkie waddled over to her, with the crinkling of her padding causing Limestone to snicker a little. Pinkie was looking increasingly miffed the closer she got to her, but she managed to keep herself from saying anything in that moment. Instead, Pinkie was helped up onto the high-chair with Limestone’s help. “Nnnghhh… Here you go, you big baby~”

Marble Pie could only watch from the kitchen doorway, with her legs inching themselves in closer to keep her padding tightly nestled against her crotch. It wasn’t nearly enough to keep the pressure at bay, but it was the best chance she had at keeping herself dry. Her eyes glanced over at the bathroom door, which was within view across the kitchen behind Limestone and the high-chair. She had no idea how she could get her way over there, or even if she could get past the lock and sneak inside. However, Marble had to struggle not to widen her eyes when she took notice of the metal key hanging by a chain right beside the doorway.

“Mmmphhh!!” Pinkie clutched her muzzle tightly with a muffled groan, while her padded backside was stuffed into the tiny confines of the chair. As she sat with her torso lurched forward, she could feel her bladder being pressed down against the padding over her crotch. Limestone didn’t hesitate to snap the serving tray back down over Pinkie’s lap, which pressed the diaper even harder into place. Pinkie whimpered and tried to cross her hind-legs together while they dangled off the floor; but alas, Limestone was quick to take notice and shake her head.

“Uhh, uhh, uhhhhhhh~” Limestone’s devious grin widened when she reached for something she was hiding underneath the table: a large bundle of rope. “Now, Pinkie… We both know I’m not gonna let you off that easy~”

Before Pinkie could try to kick her away, Limestone grabbed her flailing hooves with ease and placed them against the high-chair’s legs. Marble’s jaw dropped at how effortlessly her sister was able to keep Pinkie in place, even as the mare struggled and yelped against her grasp. Limestone’s work on the farm provided her with more than enough dexterity, as she got both of Pinkie’s hind-legs pried apart and tied against the chair’s front legs. Pinkie’s head lurched down with a heavy groan, while her padded crotch was on full display with her legs spread wide-apart.

“And since you wanna be a fidgety baby…” Limestone used more of her rope to bind Pinkie to the chair, all while Marble Pie stared in absolute shock. Pinkie whimpered worriedly, but she soon found her torso tightly pressed against the back of her high-chair to keep herself from bucking out of her restraints. By the time Limestone got to work tying Pinkie’s forelegs to the chair’s armrests, Pinkie winced at how securely that rope-work proved to be. If she wasn’t so worried about the growing pressure of her bladder, she would’ve pointed out how Limestone’s rope-work was as good as Applejack’s. Nonetheless, she was too embarrassed to say much by the time she found herself completely tied up and unable to move an inch. “There!” Limestone stepped back to admire the finished product of her hoofwork. “Heh~ Now all we gotta do is wait…”

Pinkie’s head lurched up to stare at her in shock. Both she and Marble quickly realized that there wasn’t anything on the kitchen table, meaning that Limestone’s “lunch” claim was most likely just a ruse. Granted, neither of them felt particularly “hungry” after filling themselves up with milk and taking a nap. But at the same time, the diapered mares tensed up with worry when they realized how determined their sister was to make them fulfill their punishment.

“Nnnghhh!!” Pinkie tried to move against her restraints, but it was obviously to no avail. Not only were her limbs all tied down to the chair to render her immobile, but the additional rope around her stomach meant that she couldn’t try lurching forward in her seat. Even if she did manage to move in the high-chair, Limestone was standing right in front of her to make sure there was no funny-business; plus, there was a good chance that Pinkie would just tip over and fall onto her face. She eventually closed her eyes to avoid staring at her sister’s insistent smirk. “L… L-Limestone, please! I ca… I c-can’t do it like this…”

“Oh, you can’t?~” That dire plea got Limestone to grow an especially wicked smile. She trotted away from Pinkie in the high-chair, which left Marble to look over and see how restrained her sister was. Her blush intensified when she saw how notably Pinkie’s white padding was displayed in the chair, practically staring back at her like the eyes in a creepy painting.

Meanwhile, Limestone cleared her throat to get both her sisters’ attention, just as she stood beside the kitchen sink. “Maybe this will help both of you… relax~”

With that, Limestone turned one of the faucet knobe the tiniest bit, which made a small trickle of water pour from the spout. The moment that thin stream hit the metal sink and began to pour down the drain, Pinkie and Marble groaned through their teeth at the same time. “MMMGHHH!!!~”

Limestone chuckled with a look of pure amusement, and leaned against the kitchen counter to watch her sisters squirm. Marble tried her best to keep her legs tightly closed, but her diaper was too thick to get her rear hooves to even touch together. Meanwhile, Pinkie was writhing in her high-chair while tightly restrained, and unable to even try to get in a more comfortable position. The sound of trickling water made her swollen bladder feel downright painful, and caused her breathing to grow more rapid between those harsh groans. Marble tried not to whimper too audibly herself, and hoped that her silence would be enough to keep Limestone from glancing over at her for too long.

“Oh, is there a problem, Pinkie Pie?~” Limestone walked up to her sister’s high-chair, and placed a hoof atop one of her thighs. Pinkie struggled to keep her muzzle clenched shut, but her sister could still hear her whimpering when she got in close. “Oh, look at how badly you’re blushing,” she said with a mocking jeer. “Is that because you need to go wee-wee like a widdle baby… or is that just because you’re too embarrassed to let yourself do it?~”

“HMPH!!” Pinkie tried to hang her head away from Limestone’s taunting grin. Even though she felt like her bladder was about to burst, she couldn’t deny that her sister wasn’t wrong about her humiliation locking her impulses in place. Even if she was being forced to do it, she really, REALLY didn’t want to wet herself like a little kid in some makeshift “accident.” Unfortunately, unless Limestone suddenly grew a conscience and decided to break her free, Pinkie was growing increasingly wary about how long she could stay like this.

“Well, don’t you worry about me…” Limestone kept a teasing grin as she got in front of Pinkie’s chair, and stood upright to rest her elbows against the serving tray. She brought one of her hooves down to press up against Pinkie’s padded crotch, which caused her to let out a strained moan from the building pressure. Limestone’s ears perked up from that peculiar noise, but she kept her smile unchanged in wait. “I got allllllll day to wait for you. Just like how you waited all afternoon for me to finish YOUR chores~”

Pinkie wanted to yell at her for keeping this punishment going, but she was too tensed up from the intensifying pressure to try opening her muzzle. Limestone gently rubbed at the smooth, currently clean padding that was being shown so prominently in Pinkie’s high-chair. Meanwhile, Limestone kept a direct stare on her sister’s deepening blush, and the pained grimace she had as she struggled to hold it in. Due to how sternly she was keeping her eyes on Pinkie, Marble tried her best to silently waddle around the table and out of Limestone’s line of sight. After a few long, strenuous minutes of hearing Pinkie’s groans and the sink’s trickling water, Marble was able to “sneak” past the two as covertly as she could in her crinkly diaper.

Unfortunately, as soon as she made a waddling crawl past them, she didn’t seem to notice Limestone shooting her a knowing glance with a light smirk. “Hmph~”

The faucet kept running the tiniest bit, trickling more water and causing Pinkie’s legs to strain against the ropes. Her lips were pursed so tightly together, only the faintest whimper could be heard when Limestone loomed in closer. Tears were starting to bead at the corners of Pinkie’s eyes, both from the physical and mental strains that kept her from letting loose. She tried her best to focus on her breathing, but it merely came out in feeble pants through her flaring nostrils. Marble was trembling just as badly behind her sisters, but her shaky hooves held her upright just long enough to reach up and grab that metal key…

“Come on, Pinkie…” She pressed her hoof even tighter against that diapered crotch, which made Pinkie’s muzzle finally reopen so she could groan out loudly. “If you want to be let out of this chair, I expect you to do it~”

She couldn’t pull her body forward while her torso was tied to the chair, nor could she close up her legs in any way. She tried to grit her teeth in anticipation, but it did nothing to counteract the additional pressure Limestone was giving to her bladder. Marble winced from how badly Pinkie was sounding in her bondage; but with her own bladder swelling up painfully in need of release, she tried to use her sister’s struggling as an advantage as she carefully inserted the key in the bathroom lock.

“Oh, Marblllleeeeee~”

Marble Pie froze up in horror, just as she got the door unlocked with that damn key. When she turned around slowly, her eyes as wide as a character anticipating a monster in a horror movie, she was met with the sight of Limestone staring at her with a haughty grin. She pulled away from Pinkie’s blushing face, only to turn the high-chair around so the two padded mares were facing one another. Marble may have been able to unlock the door, but she was frozen in peril when she saw her sister squirming badly in her bondage.

“I know you thought you could avoid seeing it happen, but trust me…” Limestone reached towards the sink right beside herself and Pinkie, and turned the knob so the trickling water could be a full-blown pour. Even more water loudly hit the bottom of the sink, which locked up both of the sisters’ knees and made them groan loudly. All the while, Limestone narrowed her eyes on Marble as she lifted up the high-chair’s serving tray. “... even if you try to enter that bathroom, this is going to happen to you~”

“MmmmmmMMMNNNNGHHHH!!!~”

Pinkie Pie couldn’t take it anymore. Her eyes were clenched tightly shut, and her muzzle was contorted badly enough to show how shameful and mortified she felt in that moment. Her hind-legs quivered tightly against the ropes, but they remained spread apart so her sister could see all of her padded crotch. Marble Pie’s muzzle went agape, but nothing could come out to cover the sound of that distinctly loud hiss:

‘Psssssssshhhhhhhhhhh…’

“AaaaaaAAAAAaaaaahhhhh…” Pinkie hung her head, but her blushing expression was clearly seen by both her sisters as she finally relieved herself. She looked both humiliated and relieved at the same time, while the crotch of her diaper instantly began to swell out from the gushing flow that hit the padding. The white plastic ballooned out slowly between her legs, before a faint yellowish hue started to seep through the padding and into view. Pinkie’s heavy sigh lingered on for well over a minute, but the hissing from her diaper continued for much longer while Limestone watched with glee.

“Ooh, somepony had to go~” Limestone leaned in to get a good look, and snickered at the sight of Pinkie’s diaper expanding out between her thighs. The pink mare was trembling with a faint whimper, but she couldn’t stop pissing herself until every drop was soaked into the padding. What was formerly a smooth white surface behind the transparent plastic, was now pressing tightly against the outer restraints while bloated out and a deep shade of yellow. Pinkie shuddered with a tight cringe on her face, since she was able to smell the acrid scent of her urine clear as day through her diaper. Limestone didn’t seem to mind the smell, and merely huffed before giving her crotch a playful pat. “Therrrrrre you go. That wasn’t so bad, was it?~”

If Pinkie wasn’t so embarrassed by what she just did, she would’ve shot her a deathly glare for asking such a thing. Unfortunately, since Pinkie wasn’t able to hold her bladder, there was nothing to keep Marble Pie out of Limestone’s focus for now. Her heavy blush disappeared to reveal a petrified pale, not that it deterred Limestone’s grin by any means.

“So, how about you?~” Limestone gave the high-chair a couple pats with her hoof, before tilting her head at her still-clean sister. “You think you can hold out longer tha--HEY!!!”

Before she could finish, Limestone tried to lunge in when Marble suddenly threw open the bathroom door. She may have had a disadvantage in speed with her added gait, but she was close enough to the door to rush in without warning. She slammed the door into Limestone’s face, and locked it shut before she could try to burst in. By that point, Marble was moaning out weakly as she waddled over to the toilet and tugged at her padding.

“H-HUH?!” Marble expected the diaper to be easy enough to rip off her waist, even for somepony as frail as herself. But as soon as she pulled at the elastic cuffs of the plastic pants, she was horrified to discover that they were as tightly wrapped as the packaging that ironically held scissors. Her panting grew more rapid and fearful, and she spun around a couple times like a dog trying to chase its tail. But as soon as she saw the back of her pants’ waistline, her pupils shrunk to the size of pin-pricks.

She recalled hearing a click when Limestone got her and Pinkie into the plastic pants; however, she would’ve never realized that was from a small padlock that was tightly secured around the base of her tail. She began to hyperventilate as she helplessly pulled at her shorts, but alas, the plastic proved to be far too much for the lone diapered mare to handle.

“Oh, Marble…” With that jeering voice causing her sister to shiver in dread, she wasn’t met with any opposition when she used her personal key to unlock the door from the outside. Marble could only stand with a mortified look when she saw Limestone’s cocky grin at the open doorway. She could also hear Pinkie Pie groaning out in the kitchen, but it was doubtful she could do much at that moment. Marble Pie could only breathe out shakily, before her eyes drifted down to see a new item being held in Limestone’s hoof.

“Since you wanna try being a naughty filly…”

Limestone grinned rather eagerly, and held up a shiny metal bar with hoof-cuffs at both ends.

“... now the two of you will have to keep those diapers on until you used them both ways~”

Chapter Three

“... b… b-b-both ways?”

Marble Pie was still shivering badly from her swollen bladder, which kept her hind-legs squirming uncomfortably against her padding. However, the mare was left frozen in terror while staring back at her sister’s smug grin.

“That’s right,” said Limestone rather cockily. “Since you tried to break the rules, I expect both you and Pinkie Pie to do more than Number One~”

Marble’s heart practically shot down to her stomach, and her pupils shrunk with immense worry. Back in the kitchen, where Pinkie Pie was still tightly restrained in her high-chair, she heard enough of her sister’s plans to shout out, “Oh, come on, Limestone! That’s not fair! I already peed myself!”

“And you did a very good job~” Limestone turned around to shoot Pinkie a wide, albeit gracious smile. She huffed to herself cheekily when she saw how swollen the padding between Pinkie’s legs had gotten, as well as how yellow the plastic became. Marble groaned and averted her eyes from Pinkie’s current state, which caused her to try and clench her hind-legs as tightly as she could. Pinkie was glaring at Limestone like she wanted to smack her across the mouth; unfortunately, since she was still helplessly bound to her high-chair, she couldn’t do anything but brood silently when her sister patted the top of her frizzy mane.

“How about this?” asked Limestone, before she lifted up the metal bar she was still clutching in her hoof. She used it to reach up over the top of the fridge, with one of the hoof-straps connected to its end to pull out a hidden item. Pinkie may have still been upset, but her scowl lessened by quite a bit when she saw a plastic bag of brightly-colored gummy candies. Marble looked equally as surprised, since she had no idea that Limestone was able to hide sugary treats from their sister’s senses. As soon as the bag was pulled off the top of the fridge, it fell effortlessly into Limestone’s other hoof. “Since you did such a good job, I’ll let you have some of these gummy bears as a reward!”

Both Pinkie and Marble were rightfully wary of their sister’s offer, especially since Limestone had an unnaturally cheerful smile directed towards the pink mare. Pinkie groaned a little in trepidation, but couldn’t squirm too much without making her soggy diaper squish audibly between her legs. Marble grunted a bit and tried to back away from the source of that noise, which only reminded her of her own bladder straining badly. But as soon as she tried to turn her head away from Limestone, Marble yelped out when she felt something tightly latch around one of her ankles. “EEP!!”

“Ohhhhhh, no you don’t!” Limestone’s smile turned more mischievous as she held onto the spreader bar in her hoof, and skidded Marble back into the kitchen with her hooves sliding across the linoleum. Marble trembled with a faint whimper, realizing that she wasn’t able to slip back into the bathroom while her hind-leg was cuffed in her sister’s grip. However, Limestone merely held onto the other end of the bar for a moment, before redirecting her focus towards Pinkie. “What was I saying? Oh, right!”

She opened the bag of gummy bears, which Pinkie couldn’t help staring at hungrily. Considering how long she and Marble Pie were locked in the bedroom, their growing urge to pee made them forget that they also skipped lunch. Limestone kept a satisfied smirk upon seeing how wide Pinkie’s eyes were getting, especially when she moved in closer with the open bag in her hoof. “It’s alright,” she said assuredly as she brought the clear plastic bag up close to Pinkie’s muzzle. “You did what I asked, so go ahead. Have some gummy bears~”

Pinkie was still wincing slightly, but she couldn’t help licking her lips upon smelling the artificial fruity sweetness up close. Since all of that milk had obviously gone through her system, the mare only hesitated for a moment before accepting Limestone’s offering. She leaned in like a zoo animal being fed by a little kid, and dipped her muzzle into the bag to begin munching on the gummy bears. Marble could hear a muffled “Mmm!” from Pinkie in delight, before she dove in more ravenously.

“Theeerrrrrrre you go~” Pinkie was too busy gorging on the large bag to see how much wider Limestone’s grin became. She carefully placed the bag on the serving tray atop Pinkie’s lap, which was able to stand in place while she continued to chow down. Limestone then turned back towards Marble, who had her eyes as tightly shut as her buckling legs; or at least, her legs were as shut as could be while so much poofy padding was bunched between her thighs. Nevertheless, Limestone huffed with an amused grin and shook her head. “Tsk, tsk, tsk… Marble, you’re not going to get off that easily~”

Marble Pie yelped out a second time as she felt her sister reach from behind and grab both of her hind-legs tightly. Limestone got the spreader bar positioned between Marble’s hooves, which forced her legs wide-open without any means to close them. Her head hung low with a shuddering moan, as the lack of pressure against her crotch made her full bladder completely unavoidable. The growing strain became far too immense to ignore, which made her whimper badly and hope for the slightest bit of mercy.

Unfortunately, as soon as she heard a couple metallic clicks against her ankles, and stared down to see a couple small padlocks holding the straps in place, Marble Pie knew that mercy wasn’t in her sister’s vocabulary.

“Much better~” Limestone stepped back to admire her work, with Marble already hunched over with the aid of that spreader bar. The diapered mare groaned and fidgeted against her restraints, but all it did was make her poofy backside dangle back and forth enticingly. Limestone smiled at the view of all that smooth white padding, fully aware that things would change soon enough. But before Marble Pie could get the chance to give in, Limestone went back to Pinkie Pie’s chair and pulled the bag away. “Now, now, Pinkie… A good baby needs to share, remember?~”

Over half the large bag had already been emptied, which made Limestone snicker to herself when she turned back towards Marble. Pinkie groaned a little with a disappointed scowl, but she couldn’t really complain when she was given something to eat. Meanwhile, Marble was too distracted by her own impending doom to really take notice of the bag in Limestone’s hoof. Even when she caught the smell of that sweet candy, Marble’s muzzle tightened with an obvious look of discomfort.

“It’s alright, Marble,” she said assuredly, before placing a hoof atop her sister’s diaper with a gentle pat. “Pinkie already went, so there’s no reason for you to hold back either~”

“Mnnnghhh!!” Marble lurched down even lower, and tried to push herself forward with her forelegs. However, with the spreader bar rendering her hind-legs next to useless, she could only skid a couple inches across the linoleum floor. Limestone made sure to close the bathroom door before her sister could attempt to sneak back inside, grinning eagerly all the while. Marble eventually let out a hoarse sigh, and tried to ask in a meek voice, “Can… C-Can I at least go… t-to another room, at least?”

“No.”

Limestone reached down to grab the spreader bar between Marble’s hooves, and pulled her back a few feet so she was in the middle of the kitchen. “Pinkie did it in front of us, so it’s only fair that you do the same~”

Pinkie grimaced while still bound to her high-chair, but her muzzle was clenched with a conflicted expression. Part of her wanted to speak out against Limestone forcing somepony as timid as Marble to do something so embarrassing; however, considering how she was currently tied up in rope and still wearing her wet diaper, she could only imagine what horrors Marble might face if she didn’t play along. In the end, all the pink mare could do was hang her head in silence while avoiding Marble’s exposed stance. “Nnnnghhh…”

“If you do it, I’ll give you a reward too~” Limestone held up the half-eaten bag of gummies enticingly, and perked her brows with a grin. “I’m sure you’re hungry, aren’t you?”

Even after seeing a full-grown mare piss herself in their kitchen, Marble couldn’t deny that she was in need of a snack. Of course, the pressure in her bladder was far more distracting than her grumbling stomach. She whimpered more painfully with each passing second, but she couldn’t fathom the idea of going in her diaper willingly with other ponies present. By the time her ankles quivered against the spreader bar, tears began to bulb at the corners of Marble’s eyes. “Nnnnnnffffff… a-a-a-a-aaaahhhhhh…”

Limestone waited another moment, and eventually sighed with a flatter expression. Part of her wanted to be impressed that Marble was holding it in so well; however, she was more disappointed that her sister hadn’t received her “treat” yet. Because of that, she silently walked over to Marble’s front while her eyes were closed. Pinkie’s eyes widened in worry when she noticed what her sister was doing; but before she could think to warn Marble, Limestone lunged in close to her sister’s ear and yelled out, “BOO!!!”

“EEEPPPP!!!” That sudden noise made the mare jolt up in terror, her eyes wide-open and her fur standing on end. In addition, Limestone’s little “scare” proved to be just the trick to get Marble’s bladder going. As soon as her body locked up in fright, Marble blushed and clenched her eyes with a deep, mortified whimper that made her shudder. Her knees wobbled, but the spreader bar ensured that she was standing upright for her diaper to be fully visible.

‘Pssssssssshhhhhhhhh…’

“Aaaaaaahhhhhhhh…” Marble Pie’s heavy groan sounded both relieved and petrified at the same time, although she tried her best to hide her open muzzle with one of her forelegs. Pinkie winced in pity as she saw her sister’s diaper begin to swell between her open legs. The faint sound of hissing was enough to make Limestone grin excitedly, and glance back at Marble’s rump to see the crotch of her diaper lowering by the second. The spreader bar worked like a charm to keep her backside presented, and show just how much urine was soaking into the white padding. Of course, it didn’t take long for a deep yellow hue to begin to surface between her legs. “MmmmMMMmmmnnnghhhhh…”

Limestone watched in silence with a smug smirk, looking particularly pleased with the end result of Marble Pie’s wetting. Not only did she piss herself for well over a minute, but the end result was her diaper bloating out by at least a third of its original size. The yellowish tint of her padding spread out quite a bit, only stopping halfway up her soggy rump. Meanwhile, Marble Pie was struggling not to cry as she felt how warm and heavy her diaper became. “No… No, no, no, no, no, no, no…”

“Ssssshhhhhh… It’s okay, Marble~” Limestone leaned down and kissed her sister on the forehead, showing a gentler side that made Pinkie skew her head in surprise. Marble couldn’t even pull away her forelegs to look up at her, and struggled to breathe without holding back choked sobs. Limestone brought that bag of gummy bears close to her sister’s head, and pulled back before saying, “There you go, sis! You can have the rest of that bag as a reward~”

“Nnnnffff!” Pinkie scowled a little while tied up in her chair. “What, that’s it?! That’s not a lot of candy between the two of us!”

“Well, you two are being punished…” Limestone glanced back at her with a cheeky grin, while Marble sheepishly pulled her head up to examine the open bag. After wiping her face with a foreleg, thankfully not feeling any tears against her cheeks, she sniffed a couple times before digging her muzzle into the candy. They could both hear Marble munching softly from the bag on the floor, but Limestone walked up towards Pinkie while their sister was eating. Much to Pinkie’s surprise, Limestone began to untie the ropes binding her forelegs to the chair’s arm-rests. “Besides, I have a good feeling you two ate a bit too much of that candy~”

Pinkie froze in place, and her eyes widened when she looked back at Marble eating from the bag. The packaging was clear plastic, but she was able to see that the remnants of a sticker had been ripped off. Marble Pie continued to eat the gummies, since she couldn’t overhear her sister’s voice over the crinkling of the bag. However, Pinkie’s worried stare slowly drifted back to Limestone with her blush deepening. “... uhhhhhh… W… W-What do you mean?”

Limestone didn’t say anything at first, and merely smiled back at Pinkie while Marble ate behind them. By the time the diapered mare finished the gummies, all that remained was an empty plastic bag. Limestone giggled as she picked up the plastic with her hoof, and walked over to the trashcan to throw it away. But while the lid of the can was open, she reached inside to pull out a small sticker with the labeling still readable. “Say, Pinkie… would you say that candy tasted good?~”

Pinkie Pie was too hungry to really take notice of anything amiss with the gummies. Unfortunately, both she and Marble were looking more uneasy from their sister’s sinister wording. Limestone didn’t wait for an answer from her, and walked up to hold the label in Pinkie’s line of sight. “I gotta say, I’m a little surprised that you of all ponies didn’t realize this…”

Pinkie Pie gasped in horror, which made Marble look even more scared after finishing the bag herself. As soon as their sister read the distinct detail of the labeling, Limestone turned around for Marble to read it herself. “Ta-daaa!!~”

Sweetie Treats brand Gummy Bears

-Sugar Free-

Marble Pie had no idea what made that packaging so unsettling. However, she was able to see how quickly Pinkie Pie’s face paled in realization. Unlike Marble, who probably didn’t know too much about candy and food sciences, Pinkie had heard enough horror stories about that particular type to know it was bad news. Limestone snickered devilishly as she walked away from their stunned stares, and threw away the labeling once more. “Yeah, you can thank Doctor Elderberry for ‘warning’ me about sugar-free gummies. Apparently, the replacement sweetener used in those is called lycasin. That’s a hydrogenated syrup that includes maltitol, which is a sugar-alcohol that’s recommended by doctors as a laxative…”

Now Pinkie and Marble were really worried.

“I don’t wanna scare you two, but… Heh~” Limestone went back to Pinkie’s chair, and finished untying her ropes with a grin. “Let’s just say, you don’t want to be sitting down…”

As soon as the ropes were all undone, Pinkie groaned and leapt off the high-chair like she was planning to escape. Unfortunately, due to how swollen and soggy her diaper became, the mare skidded on her spread legs and fell to the floor. The impact caused an audible squish to be heard from her padded crotch pressing against the linoleum floor. While Marble gasped with a hoof over her mouth, Limestone giggled at their sister lying in defeat. “Mmmnnnffffffff…”

Pinkie tried to pull herself up by her hind-legs, but it was to no avail. Her hooves kept skidding against the slick floor, which made her diaper repeatedly drop down and press beneath her weight. Pinkie shivered with a heavy blush, and tried her best to keep her muzzle shut to withhold her faint whimpers. But alas, Limestone could clearly tell that the sensation of that warm, wet diaper was pressing up against her sister’s nethers particularly well.

“Aaaahhhh!!~” Pinkie Pie couldn’t hold back a weak moan that escaped her muzzle, especially when she tried to hold herself up by her forelegs. More of her weight pressed down crotch-first, which made that warm and soggy padding nestle up tightly against her marehood. Limestone shuddered a little at the sight of her sister blushing from the new sensation, and her muzzle grew to a slightly envious grin. Meanwhile, Marble Pie tried her best to turn around with the spreader bar in place, and face Limestone directly.

“See, girls? It’s not all bad~” Limestone didn’t try to pull Pinkie up from the floor, and just stood behind her with an admiring grin. Marble blushed even deeper at the sight of her sister writhing on the floor, with her expression bordering between disgust and slight arousal. Pinkie’s rear hooves kept sliding on the floor like it was covered in oil, when in actuality it was just her widened gait leaving her unable to stand. Not to mention, each hard press of the padding against her nethers was causing her legs to twitch and tense up in stimulation. Her eyelids fluttered each time she tried to brace herself, only to moan out a little from the oddly comforting warmth. Luckily for Pinkie’s sake, as well as Marble as she tried not to stare too obviously, she was able to grab hold of the kitchen counter and finally pull herself up.

Limestone gave her sister a light clap of her hooves. “Nicely done, sis! For a moment there, I was thinking you liked that diaper a little too much~”

Pinkie didn’t say anything, since she was struggling to stand upright with her hooves wide-apart and forelegs gripping the sink tightly. However, she still turned her head to shoot her sister a miffed-looking glare. Limestone didn’t seem too perturbed by Pinkie’s stare, since it was accompanied with a heavy blush and her knees wobbling weakly. She was also able to see how significantly Marble Pie was affected by seeing their sister accidentally humping the floor in her wet diaper; however, considering how she just wet herself and was likely still processing things, Limestone refrained from putting any additional pressure just yet.

Besides, there was still another sister who was more deserving of a little teasing before those gummies took effect.

“So, Pinkie…” Limestone didn’t seem too worried about her trying to lunge in and attack her, mostly because that wet diaper was too large and bulky for her to make any sudden moves. Nevertheless, she still kept a couple feet between herself and Pinkie when she asked smugly, “Did you have fun down there?~”

Pinkie Pie growled to herself while clinging to the kitchen counter as best as she could. Her hind-legs were wobbling as she tried to stand bipedally; however, Limestone wasn’t sure if that was because of the maltitol in her system just yet. Pinkie looked like she wanted to say something to her sister, but she kept her muzzle shut and controlled her breathing through her nostrils. Not only was she worried what else Limestone might pull if she gave her any lip; but considering what she and Marble just ingested, she didn’t want to give any evidence of her internal distress if her voice came out shaky or weak.

“Oh, come on, sis,” jeered Limestone through her haughty smirk. “How about this: If you tell me right now that you enjoyed how that felt, I’ll consider taking it off~”

“Rrrrrghhhhh…” Pinkie Pie wasn’t usually the one to get angry, but she had to turn away before Limestone could see her upset scowl. Each breath she expelled through her nostrils was shivery, both from her frustration and the intense jittering she was trying not to show. If she wasn’t in such a distressed state, there may have been the slightest chance that she would’ve been able to admit how… not uncomfortable those gyrations on the floor actually felt. But alas, even with such a tempting offer presented by her sister, the last thing she wanted to do was believe that Limestone would actually go through with it; not to mention, she really didn’t want to admit anything that telling when she was still processing things herself.

“Oh well,” said Limestone with a playful roll of her eyes. “I guess you’ll learn to enjoy yourself soon enough~”

She casually walked past Pinkie, with her tail loudly smacking the swollen and yellowed plastic on purpose. Pinkie barely felt it due to how thick the padding was, but she still shuddered with a groan barely withheld through her pursed lips. While the pink mare quivered against the counter, Limestone turned her focus back to Marble Pie and tilted her head. “My goodness! You seem to like that view, huh?~”

“Hmm? EEP!!!” Marble Pie barely heard any of the taunting banter her sister gave to Pinkie, since her sight was transfixed on the view of that soggy diaper. Due to Pinkie’s bipedal position, her rump was sticking out quite a bit to catch Marble’s accidental gaze. She couldn’t say with certainty that she liked what she saw; if anything, it was more of the shock and bewilderment of seeing an adult in such a compromising position. Unfortunately, Marble could only assume that her staring was obvious if it was enough to be noticed by their sister.

“Heh~ I figured at least one of you would catch on this soon…” Limestone trotted up to her diapered sister, leaving Pinkie to slowly stare back at them with narrowing eyes. Pinkie took notice of the key hanging from Limestone’s neck, and then back to the counter she was currently standing at. Marble caught a split-second glance over at her, and noticed one of Pinkie’s hooves silently reaching for a specific drawer. But with Limestone coming up towards her, Marble made sure her eyes didn’t drift away and give her any warning.

“So… how about you, sis?~” Limestone went around Marble’s frozen form, and smirked when she got a closer view of her wet padding. Even with the plastic shorts still locked in place, Limestone could feel the warmth of that diaper as soon as she prodded her hoof against it. Marble tensed up and gasped silently, her hooves nearly skidding from how tightly they tried to curl up. She hung her head low in an attempt to hide her deepening blush, but it did nothing to conceal her flustered groans. Limestone grinned wider from the sounds her sister was making, which made her press even harder against that warm and squishy padding. “Yeeeeaaahhhhh… I don’t think I need to ask if you like that~”

She pressed her hoof right up against Marble’s crotch, and felt just how soaked the sagging plastic became after that wetting. Marble Pie shivered badly enough for her knees to weaken, which in turn brought more weight down on Limestone’s hoof and added to the pressure. Marble clenched her muzzle, but her lips were quivering as she struggled not to moan. Pinkie Pie, who managed to get that drawer open without a sound, stared at the two in shock when she saw how blatantly Limestone was fondling their sister’s padding.

“C’mon, admit it~” Limestone licked her lips with a sensual purr, and continued to rub that swollen crotch to keep Marble squirming. “If you tell me you like your diaper, I’ll give you the chance to take it off. Wouldn’t that be nice?~”

“Nnnnffffff…” Marble kept writhing against her sister’s foreleg, feeling the same tantalizing pressure and warmth against her marehood that Pinkie experienced by accident. Even if it wasn’t her own sister groping her wet diaper, Marble knew how wrong this all should’ve been to experience. She tried to open up her muzzle, but all she could let out was a soft moan each time Limestone’s hoof pressed up against her nethers. Her squirming caused her diaper to crinkle and squish from every movement of her thighs. But alas, she couldn’t give a legible answer to make the torment stop. “Aaaahhhhh… Mmmmnnnghhh…”

“Oh, so you don’t want to take it off then? That’s perfectly fine~”

Marble’s eyes shot open, but her gasp turned to another titillated squeak when Limestone gave a hard press to her padding. The semi-incestuous teasing she was feeling made her tense up so badly, it was almost a shock that she didn’t bend the spreader bar holding her legs apart. She eventually dropped down to the floor with her chin resting against the cold linoleum. Meanwhile, her padded rump was on full display for Limestone to continue playing with inappropriately.

“You know, that’ll be a good position to stay in later on…” Limestone grinned with her eyes narrowing on Marble’s exposing position. “Although I’ll say from experience… it’s gonna be hard not to bend your knees when it happens~”

Marble Pie groaned and tried to ignore that foreboding “tip” from her sister. She was so overwhelmed by the warm diaper wrapped around her crotch, as well as Limestone’s forceful caress, that her head was clouded in a thick fog of conflicting feelings and sensations. But above all the sharp tingles that struck her nerves, the biggest thing sweeping through Marble’s mind was a strong sense of humiliation and shame. Not just for the used diaper she was wearing, but from how hard it was for her to pull away from Limestone’s hoof -- both physically and willingly.

“Hmmmm…” Limestone paused her rubbing long enough to glance down at the padding in question. Her muzzle skewed in thought before she muttered to herself, “I could’ve sworn those gummies would take effect by--”

-SNIP!-

“HEY!!!”

While she was distracted by Marble’s moaning, Limestone didn’t realize that Pinkie was sneaking up behind them with a pair of wire cutters. The tool wasn’t exactly the best for anything thicker than wire hangers, but it was effective enough to snap the chain from Limestone’s neck in one snip. Despite the fact that she was wearing the equivalent of a piss-soaked pillow between her legs, Pinkie Pie was agile enough to swoop down and snatch the key that fell to the floor. Limestone tried to spin around and grab at her sister, but it was too late. As soon as she grabbed the key, Pinkie tried to succeed where Marble failed by escaping to the bathroom.

“GET BACK HERE!!!”

Pinkie used all her natural speed and dexterity to unlock the door in less than a second, and rush into the bathroom. Not only did she manage to lock the door behind her before Limestone could interfere, but she also wedged a bar of soap in the gap between the door and the bathroom floor. It wasn’t much, but Pinkie hoped it would give her enough time to make use of the cutters still in her hoof. She was already starting to cramp up when she reached down with the tool, and tried to cut the plastic pants covering her wet diaper. Meanwhile, Limestone was furiously banging on the door and shrieking like a banshee. “PINKIE, YOU BETTER NOT TAKE THAT OFF!!!”

“Nnnnghhhh!!” Pinkie’s teeth gritted tightly, and her hooves tried not to fumble with the wire cutters as they gnawed against her transparent shorts. It took a few tries to actually penetrate through the smooth plastic with its razor-sharp tip. Fortunately for Pinkie, that first puncture wasn’t enough to penetrate the diaper as well. Like a filly opening up presents on Hearth’s Warming Morning, Pinkie Pie desperately tried to rip the plastic as hard as she could with both hooves. Unfortunately, two big factors caused her efforts to weaken drastically:

Firstly, the plastic proved to be exceptionally thick, and surprisingly tough to rip apart with bare hooves.

And secondly, each hard pull caused her gut to start churning badly enough to make her blush.

“Oh no… OH NO!!” Pinkie started to panic, and picked the wire cutters back up to aid in cutting the plastic apart. But even as more of the plastic pants were yanked apart to reveal her wet diaper underneath, her body started to twitch and convulse from the familiar pressure building up inside. She may have not been wearing a spreader bar like Marble, but she couldn’t exactly close her legs after her diaper swelled up between them. She couldn’t even tuck her poofy tail between her legs, since it could only partially cover up her padded rump. “Mnnnnghhh!! Keep it in, keep it in, keep it in, keep it in…”

Snip after snip ripped the plastic covering away, but it wasn’t going fast enough. Pinkie eventually dropped the cutters again, and gave a hard enough pull to rip the entire backside off her shorts. With the back of her diaper exposed and ready for removal, Pinkie made a beeline for the toilet. In retrospect, she probably should have pulled away the tapes of her diaper first; but instead, the mare was horrified to discover one last obstacle Limestone left in her way. “WHAT THE?!?”

By that point, the banging on the other side of the bathroom door finally stopped. Pinkie could hear Limestone chuckling evilly, while her face paled in horror. Her eyes were unblinking and as wide as frisbees, staring down at the toilet seat lid that was firmly locked in place. On both sides of the closed lid, sturdy metal latches were put in place to ironically “baby-proof” the toilet from opening up.

“Hehehehe~ I’m guessing you noticed that little ‘security measure,’ huh?” Limestone took a calming breath while Pinkie was struggling to remove the plastic pants, and remembered the spare key to the bathroom that Marble dropped on the floor. She ignored the disappointed groan Marble made behind her, as the diapered mare face-hoofed herself for not keeping it on herself. The soap-wedge Pinkie used was next to worthless, since Limestone only needed a swift kick to pop it out from the gap and skid across the floor. By the time Limestone looked inside the bathroom, she snickered at the sight of Pinkie Pie hunched over the toilet. “Well, what did you expect? I can’t have any babies falling into the toilet and hurting themselves~”

“NNNNGHHHH!!!” Pinkie tried to ignore her sister, and stood bipedally once more so she could grip the seat lid with both hooves. But alas, try as she might to pry the latches apart, they proved to be just as secure as the locks around hers and Marble’s plastic pants. She even tried to grip the latches in an attempt to find the locking mechanism, only to discover that both of them had padlocks in place by Limestone. And to make matters even worse, Pinkie suddenly lurched down when she felt that internal pressure building up even more. “Aaaaahhhhh!!”

Pinkie had to lean down atop the toilet seat, with her diaper pointing right at Limestone and her toothy grin. Marble peeked in to see what happened, and paled immensely when she saw the toilet’s baby-proofed state; once again, she cursed herself internally for not noticing that when she was in the bathroom earlier. But with Pinkie struggling to stay upright against the now-worthless toilet, Marble’s eyes were just as locked to the sight as her sister’s. Limestone could hear enough of Pinkie’s shameful grunts, as well as the faint grumbles of her stomach, to know exactly what was bound to occur.

“Oh, goodness, Pinkie Pie… Are you about to have an accident?~”

The pink mare was clinging to the toilet for dear life, but it was basically a piece of porcelain furniture that couldn’t be used while her padded rear was facing the opposite direction. Limestone stood cockily at the bathroom’s doorway, just to make sure her sister couldn’t escape her impending fate. Marble Pie whimpered at the sounds of Pinkie’s strained groans, and tried to walk away from the bathroom while she still had the chance. But much to the mare’s dismay, Limestone made sure to pull her back in with a single hoof and nestle her close to her side. “Well, where are you going, Marble? You’re just about to miss the big show…”

Just as Pinkie clenched her eyes shut and lurched her head down with a harsher grunt, Limestone leaned in close to their sister’s ear to whisper, “And you better pay attention, because you’re going to be in her position very soon~”

Marble froze up in terror, and a heavy blush returned to her face after Limestone’s telling comment. Her sister also made sure to grasp the back of her diaper hard enough to make her gasp, and she quivered like a fallen leaf against her side. Limestone kept her eager grin pointed at Pinkie, who was trying her absolute hardest not to let those gummy bears win the battle against her continency. Unfortunately, it didn’t take long before a pained moan escaped her open muzzle, and her knees buckled badly enough to squat on the floor in front of the toilet.

“Thaaaaaaat’s a good girl…” Limestone looked downright elated by the maltitol’s effects, which left her sister kneeling with her diaper just a couple inches above the floor. And with Marble standing right next to her in stunned silence, all eyes were on Pinkie as her pink, poofy tail instinctually flagged up without warning.

“Go ahead, you big baby,” jeered Limestone mockingly through her smug grin. “Show Marble what’s about to happen~”

“NNNNNNNGHHHHHH!!!”

Despite how badly she tried to stop that impending outcome, it was to no avail at the end. Those sugar-free gummies were far too effective for even Pinkie Pie to handle, and her lack of alternatives forced her to moan out in a mixture of relief and unbridled shame. Her chin rested atop the toilet seat lid, right as her knees locked into that squatting stance. Pinkie hugged the toilet with an agonizingly long groan, but it wasn’t loud enough to conceal the muffled sounds emanating through her diaper. And with her tail still rigidly raised, there was nothing to keep Marble or Limestone from seeing that mudslide occur in full view.

“AaaaaAAAAAAaaaaahhhhh!!!” Pinkie Pie couldn’t hold it in, and the back of her diaper bloated out almost instantly when she stopped trying to resist. Her long, moaning cries of embarrassment echoed in the bathroom, which nearly overshadowed the noises coming from her diaper being filled. The maltitol certainly proved its worth, as the poor mare was forced to endure a hefty load of her mess shooting into her diaper to add to its already swollen weight. Marble Pie couldn’t look away from the view of Pinkie’s diaper pushing out just beneath her tail, or the formerly white plastic morphing into an increasingly deep shade of brown. However, while Marble tried to cover her ears to avoid hearing the disgusting squelches barely muffled behind the padding, Limestone merely watched with a mixture of fascination and vendetta.

“Aaaaahhhhhhh!!!” Pinkie’s girlish moans almost contradicted the sight of her unloading into her diaper, before the bottom of the saggy padding touched the floor beneath her. Her violently intense expulsion lasted for well over a minute, with neither of her sisters blinking even once while watching in awe. By the time she finally finished messing herself, all that Pinkie could do was slump over the top of the toilet seat while her lumpy padding hung heavily between her legs. Marble Pie whimpered to herself worriedly, even as her blush grew heavier the longer she stared at the aftermath of Pinkie’s diaper usage. Meanwhile, Limestone nodded in approval while sporting a satisfied smile.

“W-Wow!~” Even Limestone seemed impressed by the veracity of Pinkie Pie’s messing, as she fanned her face with a hoof like a southern belle with the vapors. “I must say, you… you really impressed me with that one! And to think, you almost used the toilet like a big girl~”

If she wasn’t wiped out by that bowel-cleansing, as well as the fact that her diaper felt much heavier around her waist, she would’ve had enough energy to glare at Limestone and vow revenge. But after shitting herself to such a high degree in front of her sisters, all that the mare wanted to do was close her eyes and sigh in deep, guilty relief. She slowly lifted herself back up, unbending her knees while she still leaned against the locked toilet. However, after unloading so much of her sloppy filth into the diaper, Marble and Limestone were able to see how closely the browned padding was touching the back of her knees.

Marble Pie was too stunned to speak, and could only stare at the diaper like a moth being drawn to a flame. Limestone kept a tight grip on her sister’s back, ensuring that she couldn’t pull away from her side. Pinkie panted to herself hoarsely and remained slumped against the toilet, providing a painfully ironic view of herself wearing the other toilet she was trying so hard not to use earlier. And with Marble’s muzzle tightly clenched in silence, the only sounds that Limestone could hear from her sister were an audible gulp…

… followed by an audibly loud gurgling that came from the mare’s stomach.

“Mmmphhh!!” Marble Pie lurched down and clung to her belly with a hoof, almost like she was about to experience a heart-attack. Fortunately -- or perhaps, unfortunately for her, there was nothing to distract Limestone from that sound after their sister finished with their punishment. Since Pinkie Pie was still collecting herself after such a vigorous session, Limestone carefully escorted her other sister out of the bathroom.

“Alright now… I think we both know what you have to do now~” Limestone waited until she pulled Marble Pie out of the bathroom, with her spread hooves skidding behind her like a broken shopping cart. As soon as Limestone spun around to face Marble directly, the timid mare froze in terror when she saw the ravenous gleam in her sister’s eyes.

“You can try as hard as you can to keep it in, but I think we both know that it’s gonna happen…”

After that, Limestone leaned in close to Marble’s ear, and whispered with a sensual tone to match her excited grin:

“... and I have a good feeling you’re going to absolutely love it~”

Chapter Four

Marble Pie had no idea what to say, since her mind felt just as incapacitated as her bound hooves. She could hear Pinkie Pie groaning softly in the bathroom, most likely still clinging to the toilet after filling her diaper in both ways. Marble tried her hardest not to glance back in the bathroom and see how her sister was holding up; although, the stench alone was more than enough to ensure she couldn’t turn her head. In addition, Limestone had a tight grip with a foreleg around Marble’s back, just above that sagging diaper wrapped around her waist.

“... uuuhhhhh…” Marble Pie almost didn’t realize she made that noise herself, or that her muzzle was slightly agape. Limestone leaned in a little closer against her sister’s side, not showing any revulsion or hesitancy when it came to Marble’s soggy padding. The mare was still shuddering a little from the warm diaper nestled against her marehood, as well as how exposed she felt with the spreader bar wedged between her hooves. But despite how overwhelmed she may have felt -- both from embarrassment and worry for what she was about to do -- Marble Pie eventually breathed out and tried to ask feebly, “Are… A-Are you… going to go change Pinkie?”

“Yes,” stated Limestone with an affirmative nod. “After you make use of your diaper as well~”

That clarification caused Marble to groan silently and hang her head. Even though she should’ve known her sister would include such a stipulation, she really didn’t want Pinkie Pie to wallow in her own filth all afternoon. If anything, not going herself would just add a heavy twinge of guilt the longer Pinkie was forced to wear her used diaper for Limestone’s perverted amusement. Of course, Marble’s eyes widened when she felt a sudden, sharp contortion of her bowels that made her body lock up. “Mmphh!!”

“Ooh, I think I know what that noise means!” Limestone beamed excitedly down at her sister, who was trying her hardest to turn her head away in an attempt to conceal her deep blush. Marble Pie’s muzzle was firmly clenched, but her sister could still hear her faint whimpering as she stood weakly. Since she wasn’t able to move around her spreader bar, she was struggling not to bend her knees in any way. But since she wasn’t looking up at Limestone’s insistent grin, there was nothing to prepare Marble for when one of her hooves gripped the rear of her diaper tightly.

“MMMPHHHH!!”

“Yeah, there we go…” Limestone shivered with her bottom lip bitten enviously, and smirked when she felt her sister’s wet and warm padding. Her hoof nestled in between the mare’s spread legs, leaving Marble completely vulnerable to the sensation of her marehood being put under that piss-soaked stimulation once more. She wanted to lift one of her forelegs off the floor to bite down on her hoof; unfortunately, her spread-apart stance ensured that she couldn’t do such a thing without falling face-first to the floor. So instead, all that she could do was struggle to keep her muzzle shut while squirming against her sister’s grip. All the while, Limestone purred sensually into Marble’s ear to make her shudder. “Mmmmm… How does that feel, sis? You like how warm it is?~”

Marble Pie whimpered more pathetically with her head hung low, and her lips quivering from the strain of resistance. Her eyelids may have been shut, but she could feel how badly her eyes were rolling back from the immensely tantalizing sensations hitting her most sensitive regions. She wouldn’t dare admit that Limestone’s inappropriate groping was doing anything for her, especially after seeing what became of their sister after she couldn’t hold it on. However, Marble Pie’s fur was standing on end like a petrified housecat’s as she writhed on her hooves and struggled to stand rigidly.

“Hmmmmm…” Limestone could tell how badly her sister was trying to resist the titillating feelings coursing through her system. But at the same time, the mare knew from personal experience how badly Marble’s nerves were most likely tingling while being rubbed from behind. She leaned in to slip her hoof even deeper between Marble’s legs, where every hard press elicited audible squishes instead of the dry crinkles further back. Limestone could feel the additional warmth of the mare’s piss-soaked padding right up against her crotch; meanwhile, her sister’s relentless pressure was causing Marble’s knees to buckle under her own weight.

“Ooh, you really soaked this, didn’t ya?~” Limestone snickered from the withheld groans that were muffled behind Marble’s tightly-pursed lips. She didn’t relent on her tedious hoof-flicking, which was grinding hard against Marble’s nethers and leaving her completely at Limestone’s mercy. If she wasn’t so preoccupied with keeping her knees off the floor, she likely would’ve allowed herself to openly moan from the tantalizing rubs that were causing her hips to contort against her sister’s hoof. Heck, considering how badly her stomach was starting to churn from all those sugar-free gummies earlier, Marble wasn’t sure if it was better to deal with that or Limestone’s jeering voice. “Mmmmmm… Just imagine how much better you’ll feel when you use it the other way too~”

“NFFFFF!!!” Marble Pie lurched down to the floor and squirmed even harder, with her hind-legs remaining as straight as could be in pure desperation. The growing pressure in her bowels was becoming harder to ignore, despite how well Limestone’s hoof was grinding against her marehood and distracting her conflicting emotions. Marble wished she could find a way to pull away from her sister’s forced embrace, just so she could find a toilet that wasn’t tied around her waist. But alas, the most she could do was try to keep herself from humping the floor in her wet diaper like Pinkie had done earlier.

“C’moooooonnnn, Marble…” Limestone licked her lips with anticipation, and took advantage of her sister’s more vulnerable position when she dropped to the floor. Since Marble’s padded ass was still raised up high, she used her other hoof to rest atop her back and keep her chin against the ground. With her other hoof, Limestone really dug in to rub and titillate the swollen crotch of Marble Pie’s warm padding. Marble wasn’t sure if it was the additional pressure that set her off, or the lingering fears of going in her diaper in the middle of the kitchen floor. But regardless, the mare eventually opened her muzzle just as Limestone leaned down and whispered into her ear, “I know you wanna go~”

“GnnnaaaAAAHHH!!!~” Her lumbering voice came out much louder than anything Limestone would’ve expected. But despite the mare’s raised brows, her grin widened quite a bit from hearing that first genuinely lustful response. Her hoof continued to grind and caress her sister’s padding, squishing against her nethers and making her shudder with every shivering breath. Meanwhile, Marble Pie couldn’t stop writhing on the floor with her muzzle wide-open, and her hooves skidding against the cold linoleum beneath her. “Aaaaahhh!! AAAAHHHH!!! MmmmmMMMMmmnnnghhhh…”

“Mmmffffff~ You seem to be enjoying yourself quite a bit there…” Limestone was growing antsier herself, but she made sure to keep both of her hooves on Marble before her “punishment” was complete. Eventually, Pinkie Pie was able to regain just enough energy to overcome her lingering shame, and waddle to the bathroom doorway with a look of humiliation and disgust on her face; however, she froze at the spot with a heavy blush, and her muzzle fully agape when she saw her sister being pinned down and groped mercilessly. Limestone may have been able to smell Pinkie from several feet away, but she kept her focus on Marble to continue molesting her saggy diaper and make her moan. “You know… I’m starting to think you don’t want your diaper off~”

“AHHHH!!” Marble lurched her head up from the floor with a terrified gasp. “N-NO!! I… I didn’t--”

“No, you don’t want your diaper off?” Limestone knew clear as day that her sister meant the word “No” in the exact opposite way. But as her smirk grew more perverse by the second, she was more than happy to say with malicious glee, “Well, if you wanna stay in that diaper all day, I’m sure that can be arra--”

“NO!!! AaaaAAAHHH!!” Marble’s shrill moans carried just enough fear as they did pleasure, as she struggled to find her voice between the harsh grinds of Limestone’s hoof. She struggled to breathe out quickly enough to regain her composure the tiniest bit; but alas, her voice still came out weak and shaky when she tried to protest. “P-Please, I… I d-d-don’t wanna--Nnnnnfffff~”

“What was that?~” Limestone’s mocking tone matched her sadistic smile perfectly, especially as she grinded against her sister’s padded crotch hard enough to silence her words. “You don’t wanna what, Marble? You don’t wanna use the toilet like a big girl?~”

“NO!! I wa--”

“Well, it’s settled then! Heh heh~” Limestone upped the pace of her flickering hoof, which kept anything but more strained moaning to belt out of Marble’s mouth. Pinkie was barely able to stand on her own hooves, let alone breathe while wearing a full diaper; because of that, she felt absolutely hopeless to stop Limestone from continuing her rampant assault on their sister’s soggy padding. Marble Pie eventually closed her eyes with another harsh shudder, and groaned out feebly as her marehood winked hard against the inside of her garment.

“AAAAHHHHH!!!~ MmmmmMMMMMmmmm…”

“Thaaaaaat’s right,” growled Limestone with a lecherous gleam in her eyes. “C’mon, Marble. Say it~ Say you don’t wanna use a toilet anymore. Maybe if you do, I’ll let you go…”

“AAHHHH!!~” The last thing Marble Pie wanted to do was admit something so heinous, even if it meant that Limestone would lay off her diaper-squishing and give her a moment to breathe. Unfortunately, the constant pressure held against her nethers (not to mention the internal strain she could feel from her churning gut) was leaving her head thoroughly clouded in a heavy fog of impulse and desperation. Her heart was racing from the anxiety of saying such words out loud, even though she knew she didn’t have to really mean them. But at the same time, she could only assume that by this point, Limestone’s twisted mindset would find some way to use those words against her regardless of any future consequences. “Mmmnnnnghhhh… Aaahhh…”

“What was that, sis?~” Limestone gave an especially harsh press to her sister’s crotch, which caused Marble Pie’s head to reel back and let out a heavier moan. Pinkie Pie could only stand in silence, too stunned to speak out against Limestone’s cruel form of titillation. All the while, Marble couldn’t ignore her sister’s taunting voice as she kept going. “Is there something you wanna tell me, Marble? Maybe if you did, I can let go of you for a little bit…”

“NNNFFFFF!!!~” Marble Pie couldn’t take it anymore. She didn’t want to think if it was the desperation of holding her straining bowels, or just the dire need of reprieve from her sister’s tantalizing touch. But regardless, she eventually threw her head up to shout in a shrill, distraught-sounding voice: “I… I don… I don’t want to use a toilet anymore!!!~”

Pinkie Pie cringed hard from the bathroom doorway, and slumped her head away in pity. Marble stood wide-eyed for a brief moment, looking completely stunned by the words that came out of her mouth. Meanwhile, Limestone merely huffed with a cocky smirk, and instantly let go of her shell-shocked sister. After pulling Marble back up so she was standing upright (albeit while shaking like a fallen leaf), Limestone casually trotted back towards her front so she could see her gracious smile. “See? Was that so hard to admit?~”

If Marble wasn’t so shocked and upset with herself, she likely would’ve given a strong nod of her head at the very least. But instead, all she could do was stand frozen while Limestone leaned in, and rewarded her with a small peck on the cheek. She then rested a hoof atop Marble’s shoulder, and grinned devilishly as she leaned in to add, “And just think… As soon as you let yourself go completely, I’m sure you’ll be able to say that with honesty~”

Marble Pie could only breathe out timidly, unable to hide the look of unbridled fear that left her face a garish pale. She wasn’t sure if Limestone really wanted her to feel that way, or if that was just another layer of humiliation for this ongoing punishment. But with Pinkie Pie standing nearby with the aftermath still being worn against her rump, Marble could only assume that her sister was going to remain firm on her standing no matter what. Was she actually going to follow through with keeping Marble in diapers after this punishment finally ends? Neither she or Pinkie had any idea.

Unfortunately, Marble wasn’t able to dwell on such a hallowing hypothetical for too long.

“Nnnnnghhh!!!” As soon as Limestone stopped rubbing her padded crotch, and her marehood wasn’t put under constant stimulation within her wet diaper, that strong sensation in her stomach came right back into focus. Marble tried not to lurch down in pain, but the building pressure was growing too intense to ignore. Her eyes clenched as tightly shut as her gritted teeth, and she tried to focus everything she had into keeping her tail from lifting up out of instinct. Meanwhile, Limestone just stood before her with a smug, confident grin in wait.

“Hmph~ You know it’s gonna happen eventually…” Limestone didn’t seem to worry about either of her sisters trying to escape, especially when both of their hind-legs were spread wide apart from their padding and bondage. Because of that, the mare casually exited the kitchen to acquire something out of sight. “Just wait there, little babies. I have something that I know will help Marble relax…”

Pinkie and Marble shuddered uncomfortably, and winced from how maliciously cheerful their sister’s voice sounded. Marble eventually turned her head to stare back at Pinkie, who was blushing hard after witnessing her sister’s harsh groping session. Since Pinkie’s backside was still hidden behind the bathroom doorway, Marble wasn’t able to see how brown and saggy the mare’s backside had become after her strenuous messing. She could certainly smell it well enough to make her snout wrinkle uncomfortably; but alas, Marble felt bad that she was grateful not to see it again. Fortunately, it seemed that Pinkie was more concerned with her sister’s well-being than her own.

“Marble? Are… Are you okay?”

Marble wasn’t sure what would constitute as being “okay” in such a twisted scenario. But at the same time, the mare felt calm enough to close her eyes and give a silent nod.

“Nnghhh…” Pinkie hung her head in shame, literally wallowing in her own filth as she struggled not to tear up in front of her sister. “I’m so sorry, Marble… I’m so sorry for all of this!”

“I-It’s not your fault!” Marble was surprised by how quickly that insistent reply came out. However, she was grateful to have said it with such sincerity to catch her sister off-guard. “I… I didn’t try to stop you. A-And I… I’m just as guilty…”

Marble hated admitting such a thing, but she knew it wasn’t a fact she could deny to either of them. She knew that Pinkie’s milk-indulgence would likely backfire, especially with all the work they had to do that day. Not to mention, joining in with her sister was definitely a stupid choice all things considered, even if Limestone didn’t choose to resort to such extreme measures. But before she could try to say anything else, Pinkie shot her a stern glare and stated firmly, “Marble, do NOT blame yourself for this! Neither of us deserve this, and you know that!”

“I know, I know. I just…” Marble squirmed a little as she shrugged and hung her head. Even though Limestone wasn’t pressing her diaper up against her crotch anymore, there was still enough pressure and warmth against her marehood to keep the fur along her back raised. She breathed out with the faintest shudder, and closed her eyes to keep from thinking about the repercussions of such a response to her wet diaper. After a moment, all she could do was breathe out and mutter, “I… I don’t know…”

Pinkie Pie wasn’t sure how to take that statement, especially while her sister stood with such a conflicted look on her face. She was sure that Marble was just reeling in confusion and shame, especially after being rubbed so relentlessly through her padding. But at the same time, Pinkie couldn’t help but wonder if her indirect answer was hinting at anything else…

“Alright, sis!~” Limestone trotted back into the kitchen excitedly, and was holding something that really got her sisters worried again. A long metal chain was hanging around the back of her neck, dangling over her chest like a punk-themed lanyard. As soon as she stepped past the doorway, Limestone gave an effortless twirl of one of the chain’s ends to make it swing up towards the top of the frame. Pinkie and Marble were stunned by how easily she was able to latch the end of the chain to a large metal hook that was screwed to the top of the doorway. When she let go of the chain’s other end, it was dangling a few feet off the ground, just barely touching the top of her head.

She then turned back to Marble with a more mischievous grin, and pulled out a pair of metal hoofcuffs with some pink fuzzy material around them. “Don’t worry, these are softer than they look~”

“Okay, WAIT A MINUTE!!” Even in her well-used garment, Pinkie was quick to glare at Limestone and rightfully scold her. “Limestone, this is going WAY too far!”

“Hmph~” Limestone completely ignored her sister’s surly state as she trotted up towards the frozen Marble. “It’s kinda hard to take you seriously when you’re like that, Poopy-Butt~”

Pinkie groaned intensely through her gritted teeth, her face turning a beet-shade of red. Unfortunately, she couldn’t exactly lunge in and attack Limestone when her gait was widened around the girth of her saggy padding. If anything, Pinkie was lucky enough to keep a sturdy grip against the kitchen floor, and not slip onto the linoleum for another dirty humping session. The mare took a moment to shudder uncomfortably, before looking back at her messy diaper and weighing her options; in the end, she felt far too humiliated and upset to even think of risking her position by moving too much.

“That’s what I thought~” Limestone nodded cockily to her sister’s silence, and walked up to Marble before she could try to escape. Marble gasped when her sister latched one of fuzzy cuffs around her hoof, before lifting it up to gently guide her towards the chain. Her rear hooves could only slide against the kitchen floor, not providing any grip or tension to counteract Limestone’s coaxing pull. Marble whimpered through her clenched muzzle, and blushed heavier the closer she was dragged towards the hanging chain. Pinkie could barely move in her diaper, but she tried to carefully step forward inch-by-inch for her sister’s sake. But alas, Limestone was already grinning wide when she hoisted up Marble’s other foreleg. “Here we go!”

“EEP!!!” Marble Pie felt the other cuff latch around her hoof, binding both of her forelegs together while being lifted up by Limestone’s immense strength. The chain hanging from the doorway was clipped to the middle of Marble’s hoofcuffs, and was yanked up by Limestone like she was hoisting up a piece of farm equipment. Marble wasn’t able to stand under her own weight, both because of her spreader bar and the wet diaper swollen between her legs. But with the aid of Limestone’s tension on the chain, Marble soon found herself precariously hanging by her cuffs as they were raised high in the air, and latched to the hook above the doorway to keep her in place.

“Daaaaawwwww~” Limestone let go of the chain, and smiled with satisfaction when she saw how restrained her sister had become for this “punishment”. Not only was Marble Pie cuffed and hanging bipedally off the floor, but her hind-legs were spread wide apart to keep her from trying to clench. If it wasn’t her own sister hanging in such a vulnerable state, Limestone would’ve likely found the sight to be unbelievably hot. Of course, she was still blushing with a bitten lip as she walked past the doorway to admire the diapered mare from behind. “Nnffff~ Yeah, this’ll do wonderfully…”

Limestone took a second to glance back at Pinkie, and tried not to giggle with a scoffed smirk. The pink mare had to grip the side of the kitchen counter again, just so she couldn’t skid off her rear hooves and fall ass-first onto her mushy padding. Limestone thought to herself how easily it could’ve been to place butter or oil of some kind on the kitchen floor, just to see something like that happen to her sisters; however, she also knew that was way too dangerous to even joke about. She may have wanted them to endure her punishment, but she didn’t want to hurt them. That would’ve been wrong.

“Don’t worry, Pinkie. I’ll clean you up as soon as Marble finishes here~” Limestone turned away before Pinkie could even get the chance to say anything in response. The mare shuddered when she took a moment to admire Marble Pie hanging by her hooves off the floor, with that plush white padding pointed right at her. Limestone could see her sister’s tail flicking back and forth erratically, hitting the sides of the plastic with hard smacks. Limestone pondered her sister’s state for a moment, and eventually huffed with a contemplative grin. She went over to grab one of the keys she had hidden out of sight, and walked up towards Marble’s backside. “You know what? Since Pinkie got her pants off…”

Much to Marble and Pinkie’s shock, Limestone undid the padlock that was holding Marble Pie’s plastic pants over her diaper. The clear plastic was pulled down to her knees, leaving nothing to cover the sight of her bloated and yellowed diaper from view. “Besides,” added Limestone with a cheeky shrug, “it’s not like I’m too worried about you taking off that diaper right now~”

Marble Pie groaned and trembled in her bound state, and could feel the plastic pants wrapped around her spread knees. Since all four of her hooves were tightly restrained, and she was left completely immobile at her sister’s mercy, all she could do was hang her head down and struggle not to feel so embarrassed. The only saving grace she could think of was how she was indoors with only two other ponies present; but even then, Marble felt unbelievably exposed and humiliated in her wet diaper. Her heart couldn’t stop racing, and her face was as red as could be.

And worst of all, Marble could still feel that intense tingling from her marehood winking profusely against her soggy padding.

“Now then…” Limestone stood up on her hind-legs, and got right up behind her sister. She wrapped her forelegs around Marble’s torso, clinging to her chest while her crotch pressed up against the back of her diaper. She shuddered with a soft groan in elation, and bit her bottom lip while grinning excitedly. Meanwhile, Marble was trying not to get even hotter as she felt herself so helplessly trapped in her sister’s embrace. She tried to open her muzzle to protest, but all that could come out was a weak and shaky moan. The pressure building up in her bowels was becoming more painful, but she was trying her hardest not to mess herself while Limestone was right behind her. Unfortunately, as soon as she felt one of her sister’s hooves drift down towards her upset stomach, Marble had a bad feeling that she was wanting her to do exactly that.

“Mmmm… It feels like you have a lot built up in there~” Limestone gave a firm press of her hoof against Marble’s belly, causing the diapered mare to yelp out a heavier moan in response. Pinkie Pie couldn’t waddle over towards them in her current state, even as she tried to lean against the counter and skid a couple feet across the linoleum floor. All she could do was look away from the ongoing madness, but she could still hear her sister’s deep groans nonetheless. Marble Pie clenched her eyes shut and tried her hardest not to give in; unfortunately, that was much easier said than done while Limestone was continuously pushing her hoof into her constipated gut. “Yeeeaaaaahhhh… You really need to go, don’cha?~”

“Mmmnnnghhhh…” Marble Pie’s muzzle was trembling from how badly she needed to unload. Her tail was already lifting up quite a bit with every erratic wag. However, she was struggling to keep herself in control while counteracting her sister’s forceful pushing. Limestone used her other hoof to gently pet Marble’s chest, almost as if she was trying to relax and coax her at the same time. Marble couldn’t even clench her cheeks while her legs were spread apart, and she wasn’t sure how much longer she could handle all the building pressure inside of her.

“C’mon, there’s nothing wrong with answering a simple question~” Limestone gave her sister another gentle kiss to the nape of her neck, which was already becoming sweaty from how hard she was straining in her bondage. She gave a gentle rub to her sister’s belly before saying sweetly, “It’s alright, Marble. You can be honest with me… Do you need to go potty?~”

“Nnnnghhh!” Marble Pie lurched her head down as much and she could and breathed out hoarsely before giving a feeble nod. “... mmmm… mhmm.”

“That’s better~” Limestone decided to “reward” her sister with another hard prod of her hoof against her stomach, eliciting another deep moan that left Marble quivering in her chains. Her tail lifted up even more, with the tip still wagging about weakly. Marble was tensing up greatly in her chains and cuffs, but it could only do so much while standing in such an exposing state. And with Limestone keeping a tight grip around her, there was nothing for her to do but endure those intensifying bouts of pressure. “Now let me ask you this,” continued Limestone with a more devious grin while nestling up against her sister’s padded rump. “Mmmmm… Do you think you could reach the toilet in time if I let you go?~”

Marble Pie wanted to say “Yes” more than anything else. Heck, if she was uncuffed right that instant, she would’ve tried her absolute hardest to skid towards the bathroom and get her diaper off. However, the mare also knew that her sister’s “offer” was nothing more than a trap. Not only was the bathroom door locked once more, but she was sure that the toilet seat was still latched down with those blasted locks.

Because of that, Marble Pie merely groaned in defeat before giving a soft shake of her head. “Nnnffff… Nnn-Nnn…”

“Heh~” Limestone gave another couple harsh prods to her sister’s belly to keep her squirming. “That’s right. You can’t reach the toilet in time. All you can do is just take a deeeeeep breath, and use the potty you’re wearing right now. You already used it once, so what’s the big deal?~”

There were many “big deals” that both she and Pinkie could list off the top of their heads. Nevertheless, Marble Pie was too afflicted in shame and disgust to really think of anything but the building strain on her bowels. She was twitching hard in her bondage, and her raised tail was becoming more rigid with every weakening flick. She gritted her teeth tightly, but a shrill groan could still be heard to leave Limestone grinning from ear to ear. Marble hoped that her own strenuous noises could cover up the lewd whispers her sister was making into her ear; but regardless of her resistance, she was totally helpless when it came to Limestone’s coddling.

“Theeerrrrrrrre we go…” One of Limestone’s hooves pulled away from her chest, and she leaned back just enough to place it against the back of Marble’s diaper. The padded mare moaned out from the sensual press against her garment, as well as her sister’s other hoof rubbing her stomach in wait. Her breathing came out faint and rapid, and beads of sweat could be seen trickling down her blushing face. Limestone didn’t let up on the pressure she was delivering to Marble, especially when she could tell how hard she was struggling not to shit herself right then and there. “Nnnfffffff… C’mon, sis~ Show me you don’t wanna use that big, scary toilet anymore…”

Pinkie Pie was frozen while leaning against the counter, gawking at Limestone from behind like she had turned legitimately insane. Of course, it seemed highly likely that was the case with how eagerly the mare was trying to get Marble Pie to unload in her diaper. Her hoof was pressing into her stomach repeatedly, like she was trying to pump her insides and get her bowels working overtime. All the while, Marble’s shuddering moans intensified the more that building pressure caused her hooves to curl up in her cuffs. “AaaaaAAAAAHHHH!!!~”

“C’mon, Marble,” purred Limestone sensually. “Say what you wanna do~”

“I… I wa…” Marble Pie was too overwhelmed in desperation and embarrassment to realize what she was saying out-loud. Even though she technically needed to go, she ended up moaning out, “I wan… Iwannausemydiaper!!~”

“Oh, what was that?~” Limestone’s taunting tone matched her devilish grin perfectly. “You wanna do what in your diaper, sis?”

“I… Ineedtogo!!” Marble writhed and thrashed even harder in her bondage, but it was nothing Limestone couldn’t handle herself. While her hooves continued to rub her stomach and padding enticingly, Limestone waited with an antsy grin when her sister’s voice became more strained. Marble could only let out a harsh-sounding moan before she threw her head back, and her knees instinctually bent inward when her tail flagged up high. “AAAAHHH!!! I need to… I need to gooooOOOOOHHHHH!!!~”

Marble’s muzzle tried to close shut, but all she could do was grit her teeth before groaning with that first push. “NNNNNGHHHH!!!”

Marble Pie didn’t plan to push that first hot, steamy load directly into her diaper. If anything, it seemed that her body was working on its own accord to coincide with Limestone’s dirty scheme. Pinkie Pie couldn’t even look, and reeled away from the incoming mudslide that caused Marble’s padding to bloat out almost instantly. Since Limestone’s hoof was pressed right up against the formerly clean padding, the sheer mass of Marble’s load caused the crinkly plastic to push out around her hoof. Limestone groaned and shivered in absolute delight, relishing in the intense warmth and mushiness that she could feel while Marble filled her diaper uncontrollably.

“Aaaaahhhhhh!!!~” Marble Pie was trembling in her restraints, and felt utterly hopeless as she continued to push with all her might. More and more of her filth was filling up the diaper’s backside, which caused the bottom to hang even heavier between her legs as they did before. The formerly white plastic beneath her tail quickly morphed into a deep, garish shade of brown to match Pinkie’s rump a few feet away. Even though the relief of all that internal pressure dissipating was enough to make her fur stand on end and her blush to deepen, it was accompanied with an unrelenting sense of shame and humiliation as she felt herself shitting in her sister’s embrace. “NnnnnNNNNnnnghhhh!!!”

“Mmmphhh!! Oh, that’s a GOOD girl~” Limestone looked absolutely elated with the end result, and made sure to rub the back of Marble’s saggy padding as it grew heavier and browner by the second. Much like with Pinkie’s unloading, it took well over a minute or two before Marble could let out a soft, quivering sigh of relief. Limestone eventually pulled herself off her sister’s back, and stood with a triumphant grin at the aftermath of Marble’s first messing. Both the mare and her full diaper could only hang lazily in the open doorway, much to Limestone’s approval.

“Oh, man,” she said with an excited shiver that made her beam with pride. “I can’t wait to tell Doctor Elder--”

“LIMESTONE!!!”

Due to all the insanity that had just occurred, none of the three mares seemed to overhear the front door opening up. Limestone turned around to see their parents -- Igneous Rock and Cloudy Quartz -- were standing outside the kitchen with their eyes and muzzles wide open in shock. Quartz’s travel bags fell to the floor, while Igneous’ left eye twitched in stunned silence.

Marble Pie froze up in her precarious bondage, wearing nothing but a mortified expression and her fully-used diaper. Pinkie Pie tried her hardest to slip her head away from their line of sight, not wanting them to see her in the same messy padding that her sister was wearing. Both of them were utterly terrified about their parents’ presence, while Limestone just stood without a shred of remorse or worry on her face. In fact, the mare just stood casually beside her bound sister, and smiled at her parents with a light shrug.

“Oh, hey Mom! Hey Dad! Don’t worry, I was just teaching these two babies what happens when they skip out on their chores. Whoo! You wouldn’t believe how silly they looked napping earlier~”

Igneous and Quartz just gawked at their daughter without a word escaping either of their open muzzles. After nearly a full minute of uncomfortably awkward silence, with neither of Limestone’s sisters speaking up as they wallowed in their filth and shame, the mare’s smile slowly dropped when she finally realized something was up.

“... uhhhh… did… did I do something wrong?”

Chapter Five (Epilogue)

Two Weeks Later

Pinkie Pie was walking by herself through the desolate-looking field of rocks, which were scattered all around like the tombstones of a forgotten grave. The sun was beaming down harshly upon the barren space, which made her grateful she was wearing a saddlebag with a built-in cooler for the occasion. She kept her head down so the sunlight wouldn’t hit her eyes, which allowed her to see the countless hoofprints and long lines where stones had recently been dragged around. When Pinkie finally looked up to scan the horizon, she sighed when she saw her sister off in the distance.

“NNNNGHHHHH!!!” Limestone, who was dripping with sweat and red in exhaustion, was trying her hardest to push another massive boulder across the field by herself. Usually, she would’ve had the assistance of at least one other pony to make the task easier to complete; however, the mare knew that nopony was coming to help her while she endured her own punishment. She may have already cleared two of the biggest fields since that morning, which would have amounted to a full day’s work by herself if Marble Pie was around. But after her little stunt a couple weeks ago, Limestone was expected to complete her own work, as well as her sisters’, until her court-mandated therapy sessions were complete.

“Mnnnghhhh… UGH!!” Limestone eventually slumped against the boulder with a deep, tired breath that nearly made her collapse on the ground. Her ears twitched when she overheard the sound of galloping hooves, but she chose to ignore it while panting heavily. Her eyes were closed, and her fur was beading with enough sweat to possibly water some of the plants in Cloudy Quartz’s garden. Fortunately for Limestone, she was greeted with a welcoming, almost unbelievable sight when she finally reopened her eyes. “... w… what the…”

Pinkie Pie was standing before her with a concerned look on her face, and held out a water bottle from her cooler. Limestone may have been exhausted and sweating profusely, but she quickly snatched the bottle without asking. Pinkie may have still been rightfully pissed, but she smiled in relief when she saw her sister uncap the bottle and greedily chug the entire thing in one go. After only a couple seconds of drinking, Limestone sighed hoarsely and tossed the empty bottle aside. “HUHHHH!!! Ho… Holy… I needed that…”

Limestone leaned back against the boulder, and tried to catch her breath after rehydrating herself. Meanwhile, Pinkie’s muzzle skewed a bit worriedly when she asked, “Uhhh… You know you can stop for water breaks, right? Mom and Dad told me that themselves.”

“I know, I know…” Limestone continued to breathe heavily, and eventually shook her head to fling all the sweat off her face. Pinkie reeled back with a foreleg over her face, not wanting to be hit with her sister’s sweat. Limestone eventually let out another deep sigh, but remained against the boulder when she muttered, “I just… I just wanted to get this done before sundown…”

Pinkie’s muzzle pursed tightly with an uneasy expression on her face. If it wasn’t for past events, she likely would’ve offered to help Limestone out a little. But considering how badly both she and Marble were affected by the mare’s “punishment” session, Pinkie didn’t want to give her much of a break aside from some extra water. Fortunately for Limestone’s sake, Pinkie was at least able to not scowl down at her in anger; instead, she waited for her sister to regain her strength while her muzzle was skewed in sympathy.

“S-So, uhhhh…” Limestone looked up at Pinkie after regaining her breath, and blinked a couple times in confusion. “Whe… When did you come back from Ponyville?”

“This morning, actually. I’m only staying for the night to check on Marble before heading back tomorrow.”

“Alright, that’s… t-that’s good…” Limestone nodded her head, and averted her eyes from Pinkie in guilt. Her face was already red from the strenuous work she already did, but Pinkie could tell that her sister was trying not to blush in embarrassment. She didn’t say anything, and waited for Limestone to say anything else. “So, uhhhh… is… is she okay?”

Pinkie didn’t try to show much emotion on her face, but she softened a bit when she heard her sister’s concerned tone. Regardless of what may have occurred, she was grateful that Limestone at least knew what she did was wrong. Nevertheless, Pinkie merely sighed and shrugged her shoulders. “Well, she seemed to be pretty comfortable relaxing inside. Although, uhhh… she kinda wanted to be alone for a while. That’s why I came out here.”

“Right, right…” Limestone nodded lightly, not blaming Marble one bit for needing privacy. She eventually closed her eyes, and hung her head to breathe out sharply in guilt. “Ugh! She won’t even let me be in the same room as her! I had to sleep on the living room couch for the past week!”

“Well, do you blame her?!”

Limestone’s head shot right up, and she stared back at Pinkie Pie in shock. The pink mare grew an agitated glare that Limestone hadn’t seen since the kitchen incident; except this time, there was nothing to distract Pinkie from laying in to her about her actions. “Seriously, do you have ANY idea how wrong that all was?! I was CRYING when I ran to the train station after cleaning up!! And Mom and Dad told me that Marble stayed in their bed for a week straight!!”

“I know! I know…” Limestone hung her head and tried to cover her face with both hooves. It did nothing to dissipate Pinkie’s livid glare, but Limestone tried her hardest to speak up in defense. “I’m sorry, okay?! I know it was bad now, I just… I didn’t mean for it to go that far…”

“GO THAT FAR?!?” Now Pinkie was getting really pissed. “Limestone, you held both of HOSTAGE!!! You humiliated us!!! You were getting OFF to us suffering like that!! That wasn’t just ‘bad,’ Limestone! That was… T-That was really FUCKED UP!!!”

Limestone dropped her hooves to gawk up at her sister in shock. The pink mare was still brimming furiously, not caring one bit that she just cussed full-volume at her sister. It was fortunate that they were by themselves in the rock fields where nopony could hear them; although, Limestone was sure their parents would’ve let that expletive slide in that specific case. Eventually, Limestone sighed and closed her eyes to avoid Pinkie’s livid stare.

“I… I deserve that…” Limestone spoke softly, almost mimicking Marble’s usual tone of voice. Pinkie’s angered sneer lessened quite a bit, and she tried to calm herself down when she saw how upset her sister was looking. “Look, I… I don’t blame you for being so mad at me, okay? I… I don’t have any excuse for what I did, and… a-and I fully accept how much you hate me.”

That last part caused Pinkie’s glare to disappear completely. “Whoa, WHOA! Limestone, NO! I… I don’t hate you!”

Limestone glanced up at her with a flat, disbelieving expression. That caused Pinkie to scoff and roll her eyes. “I mean, I might be mad at you for what you did, but I would never hate you! You’re still family no matter what! I just… I think I just needed to vent a little after everything that happened…”

Pinkie averted her eyes for a moment, which gave Limestone just enough time to pull herself off the rock. She cautiously walked up to her sister, and leaned in to give her a hug. Pinkie grimaced a little from how dirty and sweaty Limestone felt; but at the same time, the mare was able to close her eyes and hug Limestone back. “Hey, hey… it’s okay, Limestone…”

It took everything in her not to start sobbing into Pinkie’s shoulder. For well over a minute, the mares hugged it out in silence without anything to distract them. Limestone remained silent in her sister’s embrace, but Pinkie could hear her sniffling a couple times. By the time the two finally pulled away, Limestone quickly wiped her face with the back of her foreleg. “S-Sorry, I just… I’m not gonna lie, I was worried you would hit me or something.”

“Hmph~ Well, you should be glad I didn’t.” Pinkie tried to shoot her sister a teasing smirk, before rolling her eyes with a shrug. “I mean… if it wasn’t for what Mom and Dad told me, I might’ve actually considered it.”

“Huh?” Limestone turned back towards her with a more pulled look. “Wait, what do you mean by that? Did… Did they say something to you?”

“Well, they wrote to me after I left last time…” Pinkie motioned towards the other side of the boulder, where there was a large enough shade for herself and Limestone to perch underneath. The two sat down on the barren ground, with Pinkie pulling out another couple of water bottles. Limestone began to sip on her own, while Pinkie held hers in her hoof briefly. “But uhhh… yeah, they mentioned what happened at the courthouse earlier this month. About that ‘therapist’ you had?”

“Ughhhh…” As soon as she pulled the bottle away from her lips, Limestone grimaced bitterly while looking away from her sister. “Yeah… believe me, I’m just as shocked as you.”

“So, you had no idea he wasn’t a real therapist?”

“NO! I didn’t! None of us did!” Limestone turned back to Pinkie with an upset look on her face. “That guy was working with me for MONTHS! I told him so many of my personal secrets, just to find out he was some old pervert who wanted me to have a diaper kink!”

Pinkie didn’t say anything out loud, but she reeled her head away for a moment and thought to herself, ‘Well, he certainly succeeded there…’

“... and you know what the worst part is?” Limestone turned away from Pinkie to stare down at the ground. She closed her eyes, and sighed softly before speaking in a more saddened tone. “He… He actually helped me out a lot. Like… say what you want about his methods, but they really did make me less violent and prone to outbursts. I was able to actually stop and like… think things over logically, you know?”

Pinkie stared at her sister with a semi-sympathetic look; however, one of her brows raised when she flatly asked, “Logically?”

“W-Well, not during THAT! I already know that very well!” Limestone pinched the bridge of her snout with a hoof and shook her head. “Ughhhh… I just mean… It… It helped me…”

When she finally pulled her hoof away, Limestone kept her head away from Pinkie to keep her from seeing her embarrassed blush. “L-Listen, I… I don’t know how to say it out loud, but I don’t wanna be dishonest with you either! I just mean tha--”

“Hey, it’s okay…” Pinkie leaned in to wrap a hoof around her sister’s shoulder. “You don’t have to explain,” she said assuredly with a warm smile. “You needed a way to stop being so cranky, and you found a solution that helped. That’s perfectly fine, Limestone! Heck, I know a few ponies who enjoy, uhhh… that too…”

Limestone quickly turned her head to stare at her wide-eyed. “What!?”

“Not me!” Pinkie Pie was very quick to pull her hoof away and say that with insistence. “Seriously, I just wanna make that one hundred percent clear! But uhhhh…” She then looked away from Limestone briefly, and shrugged before confessing, “Let’s just say, I… I have a friend or two who might have, errrr… been jealous if I told them what happened…”

Limestone looked away from her sister to mouth out a silent “Whoa” through her muzzle. But before anything else could be said, Pinkie shot back at her, “But that does NOT excuse what you did, alright?! You can’t just FORCE ponies to do that kind of stuff!”

Limestone knew her sister was undoubtedly right, but she still rolled her eyes and pointed out, “Oh yeah, let me just ask somepony in town then! I’m sure that’ll work out fine!”

Pinkie looked like she wanted to say something, but she decided to drop it with a wave of her hoof. She could tell that Limestone was already guilty for what had happened, and was currently paying the price with their parents’ punishment for her. So instead of telling her something she likely already heard a hundred times before, Pinkie breathed out softly and said, “I just mean… Look, if you wanna keep doing, uhhhh… that yourself… I promise I won’t judge.”

Limestone almost wanted to say something about how their parents threw out all her baby gear, but she didn’t want to remind herself of that and get pissed again. Fortunately, the sentiment of Pinkie’s words was enough to make her glance up at her with a hopeful smile. “You… You’re serious, Pinkie?”

“Cross my heart, hope to fly. Stick a cupcake in my eye!” Pinkie Pie smiled sincerely as she made the motions of her Pinkie Promise, much to Limestone’s surprise and relief. “I promise you, Limestone. If you enjoy being padded, your secret’s safe with me!”

Limestone had no idea what came over her, but that promise was reassuring enough to make her hug Pinkie tightly. The pink mare hugged her back with no issue, appreciating the sentiment they could still carry for one another. However, as soon as the two finished hugging, Pinkie kept a tight grip on her shoulders as she shot her sister a deep and murderous glare. “But don’t you ever… EVER force me or Marble into doing that again!”

Limestone didn’t even hesitate to hold out a hoof and frantically recite the oath, “C-Cross my heart, hope to fly, stick a cupcake in my eye! I SWEAR!”

“Hmph~” Pinkie instantly went right back to smiling cheerfully, and nodded her head in approval. “Alright then! Since we got all that straightened out…”

Pinkie was the first to stand back up, and she drank her bottle of water before leaving the saddlebag beside Limestone’s boulder. “I have a few more bottles in there for you, so try to pace yourself, okay? Mom and Dad wanted me to go with them into town for some errands, but I wanted to make sure things were cool before I went.”

“Oh! Uhhh, thanks…” Limestone got herself back to her hooves, feeling significantly better after that little break to chat with her sister. She smiled when she saw the cooler of drinks, which’ll definitely lessen the time spent trotting up and down the fields for rehydration. But before Pinkie could trot back to the farmhouse by herself, Limestone tried to speak up and ask, “W-Wait! Uhhh… before you go…”

Pinkie paused and turned around. Limestone was blushing hard, but it was mostly out of guilt as she looked away from her sheepishly. “I, uhhhh… I know I screwed up big-time, so if… if you ever need a big favor to ask me… Just know that I owe you one.”

Pinkie smiled back at her kindly, and nodded without hesitation. “I’ll definitely make sure to remember that.”

With that, Pinkie hopped away from the boulder cheerfully, leaving her sister to stand all alone in the fields once more. Limestone finished her water bottle by the time Pinkie disappeared from sight, and she tossed it with a groan as she looked back at the massive rock. “Well… back to work, I suppose…”

A few hours later…

The sun was almost reaching the eastern horizon, but the farmhouse still seemed empty when Limestone finally returned from the fields. The mare was panting like a true workhorse, and was covered from head to hooves in dust and sweat. She groggily walked over to the downstairs bathroom, not even closing the door behind her before taking a long cold shower. As the mare gave herself a much-deserved cleaning, the rest of the farmhouse laid completely still.

Limestone eventually dried herself off, and grunted as she tried to trot up the stairs on weak knees. “Jeeze, how long were they supposed to be out for?” she muttered to herself tiredly. “I swear, the walk to town shouldn’t take that long…”

By the time she reached the top of the stairs, the only light she could see was beneath the closed bedroom door. Limestone wasn’t thinking clearly, and made a beeline for the room so she could collapse on her bed instead of the couch downstairs. The knob wasn’t locked, which meant that Marble Pie was given no warning for her sister coming into the room. And because of that, both mares gasped at the same time the moment they met eyes. “W-WHAT THE?!”

Limestone couldn’t say anything else, and just stood at the open doorway with her eyes nearly bulging out of her skull. Her face practically exploded with a heavy blush, and her eyes went unblinking as she gawked down at her sister. Her muzzle was agape and silent, although it was doubtful she had much to say in that particular moment. Meanwhile, Marble Pie looked just as surprised and worried as the mare staring back at her.

Marble was lying on the floor of the bedroom, with Limestone’s discarded diaper bag beside her and opened up. She was on top of the changing mat, with an opened diaper already unfolded and underneath her rump. Marble was splayed out in a full spread-eagle stance, with her exposed marehood already dusted with white baby powder. And much like Limestone, who slowly tilted her head in total confoundment, Marble Pie wasn’t able to say a word while her mouth was wide open.

“... uhhhhhh…” Limestone didn’t want to do anything too hasty, especially since she was already on the thinnest of ice with her sister. However, as her eyes scanned all the items already laid out around Marble’s pre-diapered form, her blush deepened quite a bit in realization. Not only did Marble Pie have all the diapering supplies out to get herself comfortably padded in private; but beside the open diaper bag, Limestone noticed two particular items she knew weren’t packed in there herself.

One was a small glass bottle, with the tag on the front clearly labeling it Maltitol. Exactly the same as the key ingredient in those sugar-free gummy bears.

The second was a new pair of fuzzy hoofcuffs, with the key laying right beside it for easy access.

To say the very least, Limestone was at an obvious loss for words. She couldn’t think of anything to say; but in that moment, it was clear that both of the sisters knew what was up. Part of her wanted to just back away and close the door, silently vowing to never discuss this incident with her sister again. However, her eyes darted between that bottle and Marble Pie’s face before she heard herself speak:

“.... did… did you already take some of that?”

Marble Pie wasn’t able to mutter out a peep, even after being caught in the middle of diapering herself. It took her a moment to realize what her sister meant, but she noticed the bottle of maltitol beside her diaper bag. She blushed even heavier in realization, and slowly turned back towards Limestone’s stunned stare. After a couple seconds, Marble Pie responded with a soft nod of her head. “... mhmm…”

“Oh, ummm… a-alright…” Limestone felt much less confident with herself than she had a couple weeks ago. However, the sight of her sister willingly indulging was enough to make her gulp audibly. She breathed out before taking a single step into the bedroom. Marble didn’t seem to freak out, or even look upset by her coming in closer. Because of that, Limestone decided to ask, “Do you… n-need any help with that?~”

Pinkie Pie’s threat from earlier may have been ringing alarm bells in her head; however, she distinctly remembered that her sister said not to force Marble into it again, with no clarification on consensual usage. Limestone tried to give her sister a blushy smile, hopeful that it appeared more helpful than it did hopeful. Marble Pie was still frozen atop her unfolded diaper, but her legs squirmed the tiniest bit at her sister’s question. She closed her eyes to take a calming breath, and eventually reopened them with a meager smile. She slowly reached over towards the hoofcuffs, and took them and the key in a single hoof. Before laying back atop her mat, Marble Pie blushed profusely as she held out the cuffs, and gave Limestone a nervous smile.

“... p… please~”

Limestone didn’t need to be asked twice, and grinned excitedly as she walked into the bedroom. The door was shut behind her, and only a metallic click from the lock could be heard before muffled giggling through the door.

The End

[BONUS CHAPTER]

“Ooooohhhhh… Marble, you have no idea how happy this made me…”

Limestone was getting so excited, that her hooves were shaking badly enough to nearly rip the tapes off Marble Pie’s diaper. Fortunately for both of the mares, Limestone proved to be more than capable of getting her sister’s padding securely fastened around her waist. After checking to make sure all the tapes were properly fastened, Limestone was grinning from ear-to-ear when she looked down at Marble’s blushed smile. “S-So, ummm… you feeling alright, sis?~”

Marble Pie may have been nervous about her newfound indulgence, especially since she hadn’t planned on sharing it with her former tormentor. But when she looked up at her sister, she couldn’t help but feel a little easier when she heard how flustered Limestone’s voice became. Instead of the merciless and domineering mare who forced her into diapers a couple weeks ago, all she saw was an excited sister who was wanting her to experience the same taboo excitement she clearly enjoyed herself. Marble took a moment to breathe out weakly, before nodding her head with a clearer smile. “... Mmmhmm~”

“That’s good to hear~” Limestone helped her sister up from the mat, and allowed her to stand on her hooves and feel how securely the diaper was fastened around her. Marble shivered when she looked back at herself, not seeming to mind the clean diaper around her rump like she had before. In fact, her blush deepened as she smiled with newfound contentment. Limestone couldn’t be happier about this revelation, no longer being the only weirdo in the family to enjoy such a kink. But before Marble Pie could think to say anything, her sister grinned a little wider when she held up the fuzzy hoofcuffs. “So, where did you get these from, huh?~”

Marble hung her head away from Limestone in embarrassment, mostly because they both knew those weren't the same pair Limestone used in the kitchen a couple weeks back. The mare sheepishly shrugged before confessing, “Ummm… I, uhhh… I bought them at a store the next town over…”

“Ooh, how adventurous~” Limestone looked around the bedroom while smirking curiously. Since she hadn’t been in the room for over a week, she was sure that those cuffs weren’t the only thing her sister purchased out of town. “So, Marble… did you have anything else you wanna use?~”

Marble breathed out shakily, but complied with a slow waddle towards the closet. Much to Limestone’s surprise, her sister reached into one of the closet’s back-corners before pulling out a familiar pole with two cuffs on the ends. Limestone’s eyes widened quite a bit while Marble looked away in embarrassment with the spreader bar in her hoof. “Ummm… I, errrr… I found it with the diaper bag, so…”

“Hmph~ Nice to know those bits didn’t go to waste.” Limestone snatched the bar from her sister’s grasp, and narrowed her eyes on Marble with a more devilish grin. Marble Pie blushed a bit deeper when she caught the devious gleam in her sister’s eyes; but at the same time, she didn’t try to show as much resistance as she had before. Even as her tail taied to tuck over the back of her poofy padding, Marble stood in place when Limestone lifted up the spreader bar, and spun it in the air to motion her to do the same. “Now then… how about you show me that diaper, little filly~”

Marble shuddered with a bitten lip, but complied with a light nod. She waddled herself around so her padded rear was pointing right at her grinning sister. Limestone reached down with the bar, and pulled Marble’s hind-legs apart so she could securely fasten both cuffs. Marble tried not to moan out too audibly, even though the sensation of getting in that position was already making her heart race. After both her hooves were tied and spread apart, Marble Pie shivered when she heard the jingle of those hoofcuffs in Limestone’s hoof. “Thaaaaat’s a good girl… Now, lie your chest down on the floor~”

Marble nodded again, and whimpered a little as she lowered the front half of her body. Her chest and the bottom of her chin rested against the hardwood floor, which made her diaper even more noticeable while laying in such a compromising position. Limestone didn’t hesitate to grab hold of both her sister’s forelegs, and she pulled them around Marble’s back to ensure she couldn’t pull herself back up. That time, a soft moan came out of her mouth as she felt Limestone tightly bind both her wrists together, and latch the cuffs shut with a metallic click.

“Nnnnfffff… Now that’s what I like to see…” Limestone took a couple steps back, and admired the view of her sister once again bound and tied with a diaper in place. Marble Pie closed her eyes and tried to control her breathing, but she couldn’t deny how trapped and vulnerable she felt in her precarious position. With both her hooves cuffed behind her back, and her rear-end still standing rigid with the aid of the spreader bar, Marble’s heart was thundering in her chest from the realization she was once again at the mercy of her sister. Not to mention, her tail was already flicking against the back of her clean padding, as she felt the maltitol she already ingested beginning to make its presence known.

“Mmmnnnghhhh…” Marble tensed up, and her eyes tightened shut when she felt a sharp gurgle in her gut. Her knees tried to bend inward, but she wasn’t able to close her legs and clench herself by any means. Limestone heard that muffled growl as well, and shuddered with an antsy groan while grinning behind her. She took a split-second to look back at the door, just to make sure it was locked. After that, she narrowed her sights back on Marble’s padded rear and got up close.

“Yeeeaaaahhhhh… You feeling alright there?~” Limestone reached down with a hoof, and pressed right up against the crotch of Marble’s diaper. The mare let out a sharp, shivering gasp with her eyes rolling back intensely. She shuddered against her sister’s foreleg, not caring one bit how guiltily tantalizing it felt against her winking marehood. The pressure inside of her was already starting to build up, but she was trying not to let herself unload too soon. While Marble Pie laid on the floor and endured her sister’s sensual rubbing, Limestone got up even closer so she could wrap her other foreleg around her stomach. “Mmmm… It seems like somepony needs to--”

“Limestone! Marble! We’re hoooOOOOoome!!~”

Limestone and Marble gasped at the same time, and froze with unified looks of sheer horror upon hearing their sister’s bubbly voice downstairs. They could also hear the front door opening up, with Pinkie Pie and their parents arriving back home after their errands in town. Both of them knew that in retrospect, trying something this time-consuming and inappropriate was unbelievably risky and foolish. But alas, with Marble already bound and diapered in her sister’s control, neither of them were sure how to react to the sounds of hoofsteps downstairs.

“Hey, where are you guys? We brought home dinner!”

“Oh no…” Marble Pie paled like a ghost, no longer looking enticed with her current predicament. Limestone seemed just as uneasy about their family’s return as her sister did; however, she remained straddled over Marble’s body while her muzzle skewed in contemplation. Marble was already trying to squirm underneath Limestone, but it was to no avail when all four of her hooves were tightly restrained. Even though the pressure in her stomach was building up tremendously, Marble whimpered worriedly and tried to whisper up at her sister. “L-Limestone! We… W-We need to pack everything up! Now!”

Limestone didn’t say anything, and just blinked a couple times as she looked between the locked door and Marble’s bound state. Her blush remained heavy, and her lips pursed tightly as she hummed to herself in thought. Marble Pie couldn’t see much of her sister’s expression while laying on her stomach, but Limestone’s silence was more than enough to make her worry. “L… Limestone?”

“Hmmmmm…” The mare’s gaze focused on the frail, vulnerable state that her sister was caught in underneath her. Limestone knew that if either of them got caught in that moment, they would be unbelievably screwed on multiple accounts; not to mention, she knew that her own consequences would be far worse than anything Marble may face. But at the same time, Limestone couldn’t deny how prime of an opportunity the two were presented with before their family came back home. If anything, quitting now would likely undo any progress the two were making to repair the trauma Marble experienced a couple weeks back…

Limestone thought over her options in only a few seconds, before she grew a wide and devious smirk on her muzzle. When she looked down at Marble, the mare was trying to turn her head with a paled and panicked look on her face. She could tell that Marble was petrified about being caught in a diaper again, and likely wasn’t too keen on continuing their fun. But alas, that didn’t stop Limestone from leaning down until she could whisper into Marble’s ear.

“You know… I could easily cover for you if you still did it~”

“W-WHAT?!” Marble Pie was fortunate not to have shouted that louder than a shocked hiss. “L-Limestone, no! W-We can’t!”

“Well, maybe I can’t,” noted Limestone, who pulled back just enough to shrug with a confident smirk. “I mean, if anything, I’d be in more trouble than you, right? Besides… You had to have known how risky this would’ve been for you…”

Marble Pie’s eyes widened, and her pupils shrunk in a mixture of realization and utter dread. Meanwhile, Limestone’s pervy grin returned as she felt that same exhilarating sensation she experienced during Marble and Pinkie’s shared “punishment” session. Except this time around, Marble was technically the first to start things herself; all that Limestone was doing was helping her out, and ensuring that she had a memorable experience.

“L-Limestone?” Marble’s tone of voice sounded very concerned, and she stared up at her sister seriously. “We… We really shouldn--NNNGHHH!!!~”

Her head lurched back down to the floor, and she groaned through her gritted teeth as she felt her bowels clench up painfully. Limestone took that moment to strengthen her stance atop her sister, and rub Marble’s belly with her hoof. “Sssssshhhhh… It’s alright, sis,” she purred sensually while keeping a coy grin. “Don’t worry… Nopony needs to know you wanted to do this again yourself…”

That was when Limestone’s smile grew even wider, and she narrowed her eyes on Marble while adding, “Unless… you wanted to get caught doing this~”

“W-What?! N-N-NO!!” Marbe was growing more panicked, but she couldn’t speak up without alerting her family downstairs. “Limesto--AAAHHH!!~”

Her pleas were instantly cut off by a sharp, titillated gasp the moment Limestone’s other hoof prodded her padded crotch once more. Marble’s chin rested against the floor as she writhed in her sister’s grip, and struggled to keep her head from growing clouded in taboo bliss. Her forelegs strained against the hoofcuffs, but she could barely even roll on the floor while her hind-legs were firmly braced down and spread apart. She tried to pull her head up to speak out, but the only thing that could come out of her open muzzle was a faint and lumbering moan. Limestone took a moment to make sure nopony was coming upstairs, before grinning down at her sister mischievously.

“You already gotta go, don’cha? It’ll take too long to get you out of all this before you can reach the toilet anyway. So you might as well just… relax~”

“Mnnnghhh!! I… I don’t wanna--NNNFFFF!!” Once again, Marble was cut off by her own body working against her dire pleas. Another intense bout of straining pressure struck her insides, which made her thighs tense up harshly against her restraints. Her tail was already starting to flag upwards, while Limestone continued to rub her stomach and crotch in perverted wait. Even when they were both able to hear hoofsteps nearby from the stairs, Marble wasn’t able to speak up while her marehood was being tantalized by her sister’s grinding motions. “MmmmnnnnnNNNnnffffff…”

“Yeah, that’s better,” purred Limestone, who was nestling up even closer to Marble and pressing a hoof against her upset tummy. “The sooner you go, the more likely we won’t get caught~”

‘Knock! Knock! Knock!’

“EEP!!” Marble yelped in a panic, but she wasn’t able to cover her mouth with her hooves cuffed behind her back. All she could hope to do was clench her muzzle shut, and pray to everything holy that whomever was outside the door didn’t hear that. Limestone pulled her hoof away from her sister’s crotch, just to make sure the crinkling of her diaper couldn’t be overheard.

“Marble, you in there?” Pinkie Pie’s voice was barely much of a deterrent for Limestone as she kept rubbing Marble’s belly with a randy grin. “We got takeout downstairs!”

“J-Just a minute!” blurted Limestone, who reached down and used a free hoof to cover Marble’s mouth and keep her from groaning audibly. “Uhhh! Marble and I are just talking things over! D-Don’t worry, we’ll come downstairs in a bit after washing up!”

Marble Pie winced under her sister’s restraints, and whimpered faintly around the hoof clasped over her mouth. Limestone was trying to keep quiet as well, but she was still smirking a bit as she felt Marble squirming with every press against her stomach. She couldn’t help leaning back a little, just to stare down at Marble’s padded rear with perverted anticipation. Meanwhile, Pinkie was quick to respond with a puzzled tone.

“Wait, you two are talking again?!”

“W-Well, I wanted to apologize to her!” Even though she was basically doing the same thing to Marble as she had earlier (albeit with consent this time around), Marble could hear the sincerity in her sister’s voice. “S-Seriously, after I talked with you, I decided to talk with her in private while you guys were out!”

Limestone slowly pulled her hoof away from Marble’s muzzle, and was fortunate to only hear her silently heavy breaths. Marble was blushing redder than their maybe-cousin Big Mac, but her lips were quivering in an attempt to keep herself from moaning. She was writhing badly beneath her sister, and her legs were tensing up tremendously against the spreader bar from the intensifying pressure. But even with how afflicted her bowels may have felt, Marble was able to see the insistent nod Limestone gave to motion for her to comply.

“Ummm… Y-Yeah!” Marble gritted her teeth after that weak statement, as she could feel the maltitol running its course inside of her without pause. The last thing she wanted to do was mess herself right then and there, and risk being overheard by Pinkie through the door. But at the same time, the mare really didn’t want to give their sister any cause for alarm either. So for the sake of herself and Limestone, Marble breathed out in a shaky huff and added, “W-We, uhhh… we’ve been talking things out, a-and… and I feel a lot better around her. P-Promise!”

Limestone looked down at her in surprise, her brows raised when she caught the honesty in her sister’s voice. Her eyes darted between Marble and the door before she leaned down and whispered, “Wait, do you mean that?”

“Yes, now p-please let me go.”

“Okay, okay…” Limestone cautiously pulled herself off her sister, leaving Marble lying on the floor in her diaper without any additional stimulation. She turned back towards the door with a worrisome wince, and hoped to Celestia that Pinkie could buy that excuse long enough to leave them be.

“So… everything is alright?” asked the pink mare cautiously through the door. “Because you two sound a little off.”

“Well, you saw how hard I was working in the fields!” shouted Limestone in exasperation. “Can you really blame me?!”

“I, uhhhh…” Marble had to clench her eyes shut while squirming on the floor, and was trying her absolute hardest to keep herself in control. With the last of her strength, the mare struggled not to groan from the ongoing strain when she said, “I-I was… I was crying earlier, b-but Limestone and I made up! I just… I need a moment to compose myself be… b-before coming downstairs.”

Limestone gave her sister an impressed smirk and nodded silently. Pinkie was quick to say through the door, “Oh! Uhh, yeah! Sure thing, sis! I’ll tell Mom and Dad to give you two some privacy.”

“Sounds good!” shouted Limestone more cheerfully. “Don’t worry, it’ll only take a couple minutes…”

Both of them waited a moment before hearing Pinkie’s hoofsteps fade off in the distance. As soon as Limestone counted the steps her sister made down the stairs, ensuring that she and their parents were all on the first floor, Limestone turned back to Marble with a devilish grin. “Hmph… You heard it, sis. It’ll only take a few more minutes~”

Marble Pie’s blush instantly returned, and her timid expression was made much more prevalent while bound and padded on the floor. She tried to let out a brief, whimpering groan in resistance, but she couldn’t do much in her restraints. She averted her eyes from Limestone, which just made the mare more confident as she trotted up behind her. Marble shuddered with her eyes closed before hearing her sister ask, “So, Marble Pie… you still think this is too ‘risky’?~”

Despite the coy perks of her brows for emphasis, Marble quickly huffed and shot her sister a flat glare. “Yes.”

“Well, allow me to rephrase my question then…” Limestone reached down with a hoof, and made her sister gasp once more with a hard press against Marble’s stomach. She moaned out softly with her head reeled back, but it wasn’t loud enough to cover the muffled gurgle that made Limestone’s ears twitch. Marble quivered in her bondage, and couldn’t say anything without groaning. That allowed Limestone the chance to lean in with a lustful grin, and ask Marble cheekily, “Do you think that I could get you uncuffed and undiapered quickly enough for you to reach the toilet?~”

That point prompted Marble to wince and lurch her head down once more. Her tail was fully raised, but she was controlling her breathing just enough to keep herself from unloading in her padding just yet. She knew that even thinking over her options by that point would be risky, since every second wasted would ensure Limestone’s answer soon enough. So after only a couple seconds of shuddering, Marble muttered through her teeth, “I… Idunno… Nnnnghhh…”

Her hind-legs trembled against the spreader bar, and Limestone glanced down at her diaper to see if it would sag yet. Luckily for Marble, the padding remained smooth and white against her tensed rump. Of course, that didn’t keep Limestone from smirking confidently. “Well, how about this…”

Limestone gave another firm squeeze to Marble’s belly, and made her writhe with a stronger moan which was held behind the locked door. Her body remained tightly tensed when her sister tauntingly asked, “Even I uncuffed you right now… would you want to use a toilet?~”

Limestone didn’t need to see her sister’s eyes shooting wide-open to know she got to her with that question. Marble froze in place on the floor, and her hooves stopped trying to squirm against her cuffs for a brief moment. The mare looked down at the floor for a couple seconds, before she closed her eyes with a profusely deep blush. Since she was already caught by Limestone earlier, there was no use in trying to lie. So instead, all Marble could do was lower her head against the floor and exhale weakly.

“... n… n-no…”

Before she could even shudder in guilt from confessing such a shameful thing, Marble gasped when Limestone’s other hoof pressed up against her padded crotch. She leaned in close to Marble’s ear, and said in a merciless hiss, “Then prove it. Or I’ll unlock the door so they can hear you moan~”

Marble Pie had no idea how seriously Limestone was making that threat, but it was enough to make her gasp and shiver in her grasp. She took a deep breath with her eyes closed, before her muzzle opened up to let out a long sigh of relief. “Mmmmghhhh… Aaaaaaaaahhhhhhh…”

‘Pssssssssshhhhhhhhhh…’

The faint, all-too familiar sound of hissing prompted Limestone to look down at her sister’s diaper with a pervy grin. She could instantly feel the immense warmth against her hoof while it was nestled up against the bottom of Marble’s padding, and a heavy torrent of piss soaked it to its outer plastic. Marble Pie moaned out faintly against the floor, unable to stop wetting herself due to her tight restraints. In less than a minute, her diaper hung down a couple inches between her spread legs while a deep golden hue grew across the sagging padding. “Mmmnghhhh~”

“Oooh, that’s a good one!” Limestone patted her sister’s back, smiling like a Mother pleased with her child’s potty training (or in this case, untraining). She felt confident enough to pull her other hoof away from Marble’s stomach, and stepped back so she could get a prime view of the main event. “Now then… I think you know what I want you to do next~”

Marble whimpered a little with a nervous glance back at her. Of course, since she was still cuffed and presenting her wet diaper, she knew how unlikely it’d be for Limestone to stop now. The sister trotted towards the bedroom door, and teasingly placed a hoof over the lock above the doorknob. Marble’s eyes widened, and she gasped when she saw her beginning to turn the latch. “C’moooonnnn… Either mess yourself, or I walk you down to the kitchen myself~”

Even though there was no doubt Limestone would be in deeper trouble than herself, Marble wasn’t able to think about that when such a traumatizing thought was put in her head. Not to mention, the idea alone was enough to make her heart race, and her blush to remain hot enough to practically burn her cheeks. She groaned and clenched her eyes shut, shivering badly enough to make her soggy padding dangle between her legs. She wasn’t sure what to do, but her body seemed to work on instinct the moment she heard the lock unlatch with a metal click.

“One…”

“Nnnnnghhhh…”

“TWO--”

“Aaaaahhhhh!!!~”

Limestone actually re-locked the door with that earlier click, but she was pleased with how effectively it seemed to set her sister off. She shuddered with an antsy grin the moment she witnessed Marble Pie tensing up in her bondage, before letting out a deep and strained-sounding moan. Marble’s knees tried to bend inward to get in a squatted stance, but her rump was still raised over her head by the time she finally let the messing commence. “NNNNNFFFFFF!!!”

A thick, uncontrollable mass of her filth erupted inside of her diaper, swelling out the back of her padding and causing her muzzle to hang wide-open. Her entire body quivered with her fur standing on end, and the white padding above the yellow stains to quickly sag and morph to a deep shade of brown. Limestone shuddered at the sight of every thick lump protruding and disappearing against her sister’s diaper, with the plastic continuing to bulge out and hanging heavier between Marble’s legs. All the while, Marble’s blushed and moaning face pinned to the floor was all the proof she needed that she found another pony to share this sort of experience with.

“Aaaaahhhh… Mmnnnghhh~” Marble Pie’s hefty messing session lasted for only another minute or so, before the back of her padding hung down low enough to nearly reach the back of her knees. Limestone fanned her snout from the stench, but she was smiling widely regardless. Meanwhile, Marble was laying on the floor in a relieved, taboo stupor with a faint smile still present on her quivering muzzle. And since her hind-legs were still latched to the spreader bar, there was nothing to hide the sagging bulge just below her rigidly-raised tail.

“Nnnnfffff~ Now that’s what I like to see…” Limestone made one last check of the door, as well as to make sure nopony was waiting outside, before retrieving the key to unlock Marble’s cuffs. “Alright, c’mon! We don’t have much time to clean you up, so I’m gonna be quick!”

By the time Pinkie and her parents finished unpacking all of the takeout they ordered in town (as well as putting away other groceries they purchased during their errands), none of them seemed to notice anything amiss by the time Limestone and Marble Pie came back down the stairs side-by-side. Marble was blushing heavily with a nervous smile, while her sister was grinning wide with a more satisfied expression. Both of them smelt heavily of soap and air freshener, although their parents didn’t seem to think anything unusual about that. Only Pinkie had her head tilted at the two suspiciously while seated at the dinner table. “Uhhhh… you two okay there?”

“Mmhmm!” Marble Pie quickly nodded to her sister through her blush, which seemed to only make Pinkie’s eyes narrow on them even more. Of course, the pink mare didn’t say anything when she saw how pleased their parents looked at seeing the sisters together again.

“Yeah, uhhh… I just wanted to make sure Marble and I were on better terms, that’s all…” Limestone walked towards the table first, and sat herself down with a casual smile. “And, uhhh… don’t worry about me trying anything stupid or nuthin’. I promise, I’ll keep doing the chores until that therapy stuff works out…”

Igneous and Quartz didn’t say much, but they smiled back at one another with looks of relief. Pinkie continued to stare at the two as they sat down next to each other, with Marble barely flinching beside her former/current tormentor. Sure, she still seemed a bit skittish, but that was to be expected. Meanwhile, Limestone shot Marble a warm smile to counteract the sly wink she gave out of their parents’ line of sight.

“So, uhhhh… Marble?” asked Pinkie with the slightest twinge of caution. “Does this mean… that you and Limestone can sleep in the same room again?”

Both of them blushed at the same time, with their smiles appearing a bit more flustered than before. Limestone glanced over at her optimistically, and was happy to see Marble nod to Pinkie’s question.

“Yeah, I… I think I can do that…” Marble smiled back at Limestone, and gave a secretive wink of her own. Limestone huffed with a smirk, and sighed contentedly while thinking to herself:

‘Oh man… I really hope that the child-proofing locks are still in that bag~’

The End (for real)