Limestone's Lesson

“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)