Sissy

by FabulousDivaRarity

Rating: mature
Tags: Princess Celestia, Slice of Life, Princess Luna, Drama, My Little Pony: Friendship is Magic
Length: 3689

Princess Luna becomes an Adult Foal. Celestia is there to help. Contains ABDL/Infantilism.

Princess Luna becomes an adult foal. Her sister, Princess Celestia, becomes her caretaker. Contains ABDL/Infantilism/Ageplay and sisterly fluff! Rated M for adult baby themes. Don’t like? Don’t read.

Published 2018-07-04 09:50:06 UTC
Last updated 2018-07-04 09:50:06 UTC

Sissy

Princess Luna had discovered her own love of foalish things quite soon after coming back from her banishment to the moon. She had been at a recent party celebrating her return in Canterlot, and had excused herself to go and perform her royal duty of raising the moon. As she stood on the balcony of the castle, she happened to look down towards the streets of Canterlot. There, she saw a young family walking down the street. A young mare and colt were walking alongside their foal, who couldn’t have been older than three. The little colt was carrying a plush bear on his back, and judging from his body language, he was talking to it and playing with it. But the thing that caught her eye was that the little one was still sporting a diaper. Her mind flashed through a few reasons for why this could be, the one making the most sense to her was that perhaps he had a medical condition that made him incontinent. She nodded to herself, satisfied with the answer. However, she couldn’t take her eyes off of the little colt. His innocence, his capacity for play, and his sheer joy was something that had been ripped away from her long ago. She longed for the times when she could have been like that. Her eyes stayed locked on the diaper, though. She found herself wondering what it would be like to wear one. The thought didn’t last long, though, as the young family turned a corner and was gone from her line of sight. She pushed the thought aside and returned to the party, not wanting to keep her guests waiting.

However, later that evening as she prepared for bed, she found her thoughts wandering back to that diapered foal. She fantasized about what it would be like to wear a diaper. How it would feel, How it would look, and how it would sound when she walked. She imagined that it must have felt like wearing a cloud. She pictured herself wearing one, imagining a soft, comfy diaper encasing her flank. However, she quickly snapped herself back to reality. She tried to shove the intrusive thoughts aside, and told herself she was ridiculous for even imagining such things. She managed to sleep that night- how, she didn’t know- but that didn’t stop the fantasy from entering her thoughts when she had spare moments or mindless tasks during the day, and the thoughts came back with a vengeance before she went to bed at night. Weeks went by, and she did nothing, but the agitation with the desire was slowly building until one day she decided that she couldn’t take it anymore.

She had to try this out for herself.

So, one night while the rest of the castle was asleep, and the dreams of the citizens of Equestria were pleasant enough for her to be away, she snuck out of the castle and went to a nearby shop that was open all night and sold adult diapers and other various products for incontinence. She had changed her appearance on the outside so that no pony would recognize her. She browsed the aisles until she found what she was looking for. A large pack of adult diapers in her size. She also grabbed some baby powder, wipes, and rash cream. Timidly, she picked up the package and made her way to the counter, with none of her usual confidence present. The cashier made small talk with her, and she casually mentioned that the diapers were for a donation to the local senior center so that any suspicion of who they were really for would be thrown off of her. She paid the cashier quickly and calmly made her way out the door. Once she was out of view from the store, however, she galloped home. Once near the castle, She imagined her room and teleported the package into her bedroom. Then, transforming herself back to her normal appearance, she went inside the castle. The hallways were mercifully empty, and she flew like a bullet back to her bedroom. She excused the guards who usually guarded her room and had them take the night off. Then, when she was certain they were gone, she went inside, heart pounding in anticipation.

There, on the bed, were the package of diapers.

She shut the door quickly, then secured the room to make sure no one could see inside or hear what she was doing. Then, she slowly made her way over to the bed, and picked up the package. Her heart raced faster if that was even possible, and she took a deep breath to steady herself. Then, carefully, she ripped open the package and pulled out a fluffy white diaper. She held it for a few moments, appreciating the smooth texture on the outside, before she unfolded it. Then, laying on the bed, she put it on. Just from laying on it she could feel the comforting softness, and she quickly powdered herself and pulled up the front of the garment and taped up the sides. Then, she stood up and reveled in the sensation.

It was exactly like she had imagined it would be. A soft, puffy cloud around her waist. But more than that, there was something about wearing the foalish garment that made her feel incredibly safe and secure. It was like nothing could hurt her while she was wearing this. She felt invincible. Then, realizing that she hadn’t seen what she looked like yet, she decided to go over to the mirror and see. The bulk of the diaper made it much more difficult to walk, and she found herself slowly waddling over to the mirror. However, what she saw in the mirror made her heart stop dead inside her chest.

Looking in the mirror, she didn’t see Nightmare Moon, nor did she see a princess bound by royal duties. Instead, she saw a happy, carefree, overgrown foal. The sight made her giggle, and she couldn’t help but think how infantile it made her seem. She turned around to get a better look at her diaper. She stood there, lost in her reflection for a long while, when finally, a thought, that didn’t seem to be hers at all, entered her head that snapped her out of her daze. She thought that if she was going to look like a foal, she may as well act like one.

But the question was, where did she start?

Her experience with foals was somewhat limited. Certainly there were foals in Canterlot and sometimes at events she and her sister attended, but she had never actually spent any time with them. She’d only ever observed them from a distance. She’d never done more with one than hold it or, if the situation called for it, kissed it on the cheek. She’d never considered herself likable or personable in any sense, and foals tended to pick up on those subtle signs. They sensed her discomfort with them and seemed to return the feeling.

Now, in this moment, she pulled forth every memory she could find about her few and far between interactions with foals, and compiled a list of traits. She thought it best to start with something simple: Foals crawled everywhere. So she got down on her stomach and crawled forward on the plush carpet of her bedroom. The feeling of the carpet brushing against her underside made her giggle, and it made her feel even more infantile. She crawled around the room, listening happily to the crinkling sound that her diaper made as she did so. The feel of the diaper and sound of it crinkling made her so happy that she didn’t even realize that she was cooing to herself, much like a real foal would. When she did notice, she blushed, but didn’t stop. In fact, it gave her a new idea, and she began babbling gibberish to herself.

When she got bored crawling, she moved on to the next thing she had seen so many foals do: Play. But what would she play with? Then, like a bolt of lightning, it hit her. She crawled over to her bed, still babbling as she went, and pulled out a box from underneath. The wooden box was worn with age, and bore the symbol of her cutie mark on the top. She opened the box and began rummaging through it, trying to find what she was looking for.

The box held what few childhood memories she had. There were bits of old tapestries from her first home, a few small paintings from her renaissance days, and finally, what she was looking for. Her old stuffed animal. A bear she had named Midnight. The black teddy bear was old, well over a thousand, but a few handy preservation spells had kept him from any real damage. Now, seeing her old stuffed friend brought back a tidal wave of memories, and She floated him into her hooves before pulling him to her muzzle and sniffing his fur. He still smelled like her childhood home. The scent brought back even more memories, and she smiled and pulled him to her chest.

“Hello, Midnight. I’ve missed you.” She said quietly. She hugged the bear a few seconds more before pulling away. Then, she realized that she had been using what her now more childish mind had dubbed “grown up words”. Seeing her slip, She started using baby talk to talk with her bear instead. “Middie, What we pway?” She asked the bear. She held him up to her ear for a few seconds, hearing an answer. “Sissy can’t pway wif us. She’s sweeping.” She replied. “We tink of someting else.” She listened again to the bear, and nodded at his “Suggestion”. “Otay. We pway house. I getta be the big sissy!” She said, and began to play.

She focused on her playtime for a good hour or so, barely even realizing the pressure that was building inside of her bladder. When she finally did notice, she found herself with a dilemma she hadn’t been anticipating. Theoretically, she should have thought about this possibility before she had ever bought the diapers. She should have known that this would come eventually. She just hadn’t thought it would come so soon.

Looking back, she would always remember this moment as the crossroads of her life. The point of no return. If she decided to use her diaper for it’s intended purpose, she knew she would destroy the dream of acting like a foal with a harsh dose of reality tainting her ideal fantasy. But if she didn’t use it and went to the toilet, then she would have wasted a perfectly good diaper.

The seconds ticked by and her bladder was getting fuller with every one that passed. Indecision warred on her face, and she wasn’t sure what to do. Before long, her bladder was screaming for release. Still, she remained a statue, frozen in time. She moved her head and looked down at herself. Here she was, playing with her teddy bear and wearing a diaper. She looked like a foal. So why couldn’t she have an accident like one? It was that thought that made her decision clear. She plopped down on her padded butt and started playing again. She was just too little to use the big girl’s potty. That’s why she had her diapers. The pressure skyrocketed after she sat. She tried to relax, but some part of her subconscious wouldn’t let her go. Thousands of years of being potty trained told her that she couldn’t just wet herself. The rational, adult part of her brain kept telling her to take off that diaper and use the bathroom. But the larger part of her, the foal in her that occupied her mind the most at the moment, told her that she was just a baby. And babies wet their diapers all of the time. She set Midnight on the floor in front of her. Some obscure instinct hidden away deep inside told her to put her hoof in her mouth, so she did, and started to suck. She closed her eyes and focused on the sucking. She became so engrossed with that that finally, in a burst, her bladder released.

She didn’t realize it was happening until she heard a faint hissing sound and felt her bottom grow warm. She opened her eyes, still sucking her hoof, and watched the yellow discoloration form on her diaper. It fascinated her, and she watched the whole thing unfold with a scientist’s curiosity. When it was over, she looked over to Midnight and giggled.

“Uh oh!” She said. “I make a pee pee in my diapee!”

She shifted around on her butt, feeling the squish of the soiled diaper beneath her. It felt nice. Incredibly nice. And she felt so safe and secure. She had had an accident like a real foal, and the diaper had been there to make sure there was no mess. She rolled around on the floor, enjoying the sensation of her warm, wet diaper, and babbled childishly to herself. Then, she went back to playing with her bear.

It wasn’t until her diaper began to grow cold and clammy that she contemplated giving herself a change. Reluctantly, she got another diaper from the pack and began the work of changing herself. She removed her sodden diaper and wiped herself clean before magically moving Both the diaper and wipes into a nearby lidded trash can. Then, she slid a new diaper underneath herself, spread some rash cream to make sure she didn’t get a rash, and powdered herself before taping up the diaper. Satisfied that she was now fresh and clean again, she grabbed midnight with a yawn. It was almost time for the sun to rise now, and she supposed she’d better get to bed. She slid the diapers beneath her bed alongside her wooden box, and crawled under the covers. Just before she fell asleep, one thought glowed like neon inside of her mind:

She had to do this again.

When she woke up, She opened her eyes to see her bear in her grip and realized her other hoof was in her mouth. She took it out with a pop. Seeing that reminded her of the night before, and she blushed. She looked under the covers to see her pretty diaper still snugly taped between her legs. She sighed, realizing that she would have to take off a perfectly good diaper. But just then, her bladder twinged, and she realized that she didn’t have to waste it. Her mind still half asleep and logy, she found it relatively easy to just let go and wet herself. She basked in the warm feeling for a few moments before she sighed, and realized that indulging in this new world of hers would have to wait. For now, she had princess duties to tend to. She climbed out of bed and waddled her way to the ensuite bathroom, where she disposed of the diaper, and then took a long bath, thoroughly cleaning herself off. Then, she prepared for the day ahead. With a longing look at her bed, she exited her room and let herself be carried away by the slave of duty.

However, her day would not start out the way she planned. Today was supposed to start with a meeting with delegates from Saddle Arabia, but the meeting had been cancelled due to an outbreak of Horsey Hives. So, Luna had about two hours to herself before her duties actually began. And she knew exactly what she wanted to do with her spare time. She flew from the castle over Canterlot, and transformed herself yet again into a different looking pony. This time, however, her stop was at a Children’s store. She found everything she could think to want. She grabbed herself some bottles, pacifiers, a rattle, crayons, a coloring book, some stuffed animals, and some other toys. She paid for her purchases and then flew off to the castle, landing on her balcony. She hid her new things beneath her bed and then went to really start her day.

The night seemed to pass by at a snail’s pace for Luna, but finally, her list of duties was complete. After checking to make sure that everypony was having sweet dreams, she began to indulge in her foal play. She diapered herself quickly this time, and then immediately dove under her bed. She grabbed the pacifier from her bag and stuffed it into her mouth and began sucking. Happily, she got out some of the toys she’d purchased and began to play. She built a tower with her blocks and made her new stuffed gorilla knock it down. It sent her into peals of laughter, and she was thankful the room was soundproofed. However, she couldn’t help but feel like something was missing. She certainly felt like a foal, but the room she was in didn’t make her feel like one. So she decided to fix that. A little construction spell she’d learned a while ago easily transformed her room into an adult sized nursery. There was a crib, changing table, toy box, and high chair. An enchantment made sure that the room would change back to what it normally looked like before she would wake the next day, ensuring that Nopony would ever see this place but her. When she was satisfied with her new nursery, she climbed into her new crib and she moved on to coloring. The book she got was all about animals, so she spent her time coloring a spotted dog. When she was done, she sat back and admired her work. For a single, fleeting moment she wished her sister was here to tell her what a great job she had done, but the thought quickly faded away. She found herself getting thirsty, so she pulled out one of the bottles she’d bought and used her magic to fill it with warm milk from the kitchen.

“Baba!” She giggled. Once it was full, she pulled it into her mouth and began to nurse at the nipple. The warm milk filled her and quenched her thirst. She was so focused on drinking that she didn’t realize that she had to go to the bathroom. With no warning from her mind, she began to wet herself. She was startled from her drinking by the warm sensation spreading beneath her, and was in total shock. How could that have happened without her realizing?! She felt embarrassment creep up on her, and before she knew it she was crying. Wailing to herself.

Even though she knew the room was soundproof, she couldn’t stop herself from calling for the one person who could make her feel better in this horrible moment, and cried out,

“Sissy!”

Celestia sighed as she made her way through the castle. She had woken up early in the night and found it impossible to go back to sleep. She had been in the kitchen getting herself some tea, when a familiar feeling tugged at her. Ever since her sister had been turned back from Nightmare Moon, the bond between them had grown immensely. She had become able to sense when her sister was in distress. The feeling of her sister’s distress came in a sharp pang, and she dropped her teacup to the floor, where it shattered. She galloped to her sister’s room and used her magic to open the door.

She was woefully unprepared for what she saw.

Luna sat on the floor, crying in a used diaper, in what seemed to be a giant nursery. She didn’t have a chance to contemplate the nursery. She was too focused on her sister.

“Luna?” She asked, quietly. Luna looked up at her, eyes filled with tears.

“Sissy?” She asked, eyes wide and innocent. Then, reality seeped in, and she used her wings to cover her face in shame.

Celestia was incredibly confused by what was going on here, but she was far too concerned with her sister to care. She went over to where Luna sat, and moved her wings so that she could see her face. She ran a tender hoof down Luna’s face. This display of affection sent the Princess of the night over the edge, and she leapt into her sister’s arms, sobbing.

“I-I’m s-sorry, sissy. I-It was an a-accident.” She sobbed.

Celestia hushed her. “It’s alright.” She soothed.

They held their embrace for a long time, until Luna had calmed. Celestia pulled away.

“Come on, little sister. Let’s get you changed.” She said, calmly, taking her sister by the hoof.

Luna sniffled, but allowed herself to be led to the changing table, where the package of diapers had been temporarily set for the time being. Luna laid back on the table, and wiped her eyes with one hoof. Celestia was quick to dispose of the soggy diaper, and changed her sister with easy grace. When the change was over, Luna sat up but looked down, afraid to look her sister in the eye. Celestia lifted her sister’s head and smiled at her.

“Luna, what is going on?” She asked as gently as possible.

Luna shut her eyes nervously. She didn’t know how to say this.

“You can tell me. I won’t judge.” She promised.

“I just… I saw this foal the other day.” She began. “And I… I wanted to try… Well…” Luna blushed. Celestia smiled.

“I understand.” She said. She didn’t understand the desire entirely, but she would always support her, no matter what. “Luna, I’d be happy to help you with this.” She said.

Luna finally looked up. “R-Really?”

“Of course. I love you, Luna. I’d do anything for you. You can count on me.” She swore.

Luna felt a swell of emotion unlike anything she had ever felt before. She jumped into her sister’s arms.

“I love you, Sissy.” She said into Celestia’s chest. Celestia put a hoof on her back.

“I love you too… LuLu.”