Limestone's Lesson

“... 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~”