Twilight set the last of her books on the desk, doing a quick glance over her study station to make sure she had everything ready for her weekend. Spike had just left for an excursion with Smolder to the Dragon Lands, and Starlight was visiting Sunburst in the Crystal Empire, leaving Twilight to her own devices for the entire weekend. And what better way to spend such a weekend than to catch up on all the studying that her princess duties and job as principal had kept her from. It would be such a relaxing change of pace, and she couldn't wait to get started.

Books, check. Quill and parchment for notes, check. Snacks and water to ensure that she would not need to leave her desk for anything, check. Twilight was ready for her three-day long study vacation with no interruptions!

Until a small growl from her lower half reminded her she still forgot something.

Twilight groaned; it figures that she's need to use the bathroom just as she was getting settled in. She turned to walk towards the castle's nearest bathroom, but stopped as she looked over the rest of her weekend supplies. She had made every other preparation to ensure that she didn't have to leave her desk, why should this be any different? sure, she could just head to the nearest bathroom, but not only was it several minutes down the hall from her study,she'd have to do it several times throughout her study session, and that time adds up very quickly. There must be something that she could use to remedy her situation...

A glance towards a small closet in the library gave Twilight an idea: she always kept a small pack of diapers here for whenever she was babysitting Flurry Heart. It wasn't the most ideal solution, and Twilight hesitated for a moment at the thought of openly wearing and using a diaper, but she ultimately decided that it would be worth saving the trips through the castle. Besides, nopony would be back in the castle for at least a few days; it's not like anypony would find out she had used them.

She gently levitated the pack of diapers out of their hiding spot in the closet and set them underneath her desk, pulling one out as she did so. As she levitated it before her, it did occur to her that might too small to fit on a grown mare, but it was worth a try. She undressed and attempted to secure the diaper around her own waist, succeeding with a little bit of effort. It was very snug, and while it fit, it was still rather uncomfortable and would certainly prove to be a distraction from her studying. Twilight believed she had a solution for this. Activating her magic, she cast a spell that made the diaper she wore increase in size, enough that she was sure it would fit her frame, if not still a little tight.

With the diaper now securely around her waist, she could feel its crinkly padding pressing firmly against her pussy lips. It felt unusual, but not unpleasant; it actually felt slightly arousing. Twilight pondered for a moment if this might also prove distracting to her reading, but that notion was interrupted by a small pressure build in her lower intestines. Twilight decided to test her idea before she settled in to study for the afternoon. With a small grunt, she began pushing the turd out of her ass and into the waiting diaper.

It was a rather small shit, just enough that Twilight felt the pressure within herself ease, and a small lump in the bottom of the diaper. Still, Twilight couldn't help but feel a slight rush of adrenaline as her shit tapered off of her ass. Something about not using the bathroom like she normally would was kind of exciting. Now wasn't the time to get hung up on that, though. She had proven the diaper would hold, now she just need to be sure she could sit comfortably.

She sat back in her chair, reaching behind her and pulling up the lump in her diaper to sit it behind her and make sure she didn't smear it underneath her butt. Thankfully, its small size made it easy to adjust; she could casually sit in her diaper without having to worry about it pressing against her ass too much. Confident in her solution, she settled into her seat and opened a book to begin studying.

Twilight could hardly focus anymore.

While the diaper helped to prevent her from having to leave to the bathroom, two or three wettings have left the diaper moist, warm, and extremely arousing. Twilight wasn't really sure why this was turning her on so much, but as she was gently grinding the front of the diaper against her seat and pressing the soaked padding against her pussy lips, she didn't really care. The pressure behind her had started mounting again, faster than she had anticipated, and she was eager to release it. Her left hand danced around the waistband of the diaper, lightly teasing herself above her moist entrance, wanting to pee herself again, but having nothing left in her bladder despite how much she had drank over the past couple of hours.

An idea came to her head. If it was possible to increase the size of her diaper, would it be possible to increase the volume of piss that was within her body? Twilight flipped through the books on her desk, her attention only half focused on potentially finding an answer to her inquiry, the rest drowning in her arousal at the thought of soaking through her diaper with an excessive amount of urine. Finally, one of the books gave her what she sought, and she cast it without a moment's hesitation.

Within seconds, the pressure in her bladder skyrocketed, and she immediately released the contents within, flooding her diaper in a torrent of hot piss. She stuffed her hand down into the folds of the padding, fingering her pussy as the urine coated her hand. She felt the piss start to seep through her diaper, forming a small puddle on her seat, urging her to grind her diaper into it even harder. The pressure she put on the diaper's padding forced some of the pee it absorbed to squirt out, growing the puddle she was sitting in. The trickling piss was soon joined by her immediate climax, coating the padding in her slick juices, only adding to her orgasmic high.

Twilight leaned forward over her desk, her hand resting between her pussy and the soaked diaper, the inside of her legs coated in a mix of piss and cum, and the padding pillowed out beneath her. The back corner of her mind felt ashamed of herself for making such a mess of herself, her seat and her study, but she couldn't really care less at the moment. She was actually considering casting that spell again, just to see how much of a mess she could make.

Her ecstasy and fantasy was interrupted by a sharp spike of pressure in her bowels, as she felt her anus preparing to release a massive load into the backseat of her diaper. Twilight's head rested on her books as she felt the log prod against her anus, her attention drawn to the spell she had cast and the note that it increased the volume of all excrement of the target. Oh no.

Twilight's now massive shit began to force its way out of her, filling every crevice of her snug diaper and tenting the padding so much that it pressed against the back of her chair. Twilight gripped her desk, grunting heavily with each push of her poop. The excessive amount of shit started stretching the diaper to its limits, squishing the padding inside and squeezing any urine it had absorbed out and onto the floor of her library. Twilight could feel the leg holes of her diaper stretch and pull away from her thighs, giving any passerby a clear view of the monumental mess that threatened to spill out from the newly formed windows to her crotch.

She wasn't sure how long she spent shitting herself, all she knew was that by the time she was done, she was sitting in an enormous diaper, her ass completely covered by her own waste, and her arousal returning with a vengeance. Twilight carefully lifted herself from her seat, feeling the sheer weight in her diaper warring with the grip her shit had on her ass cheeks before finally peeling away from her and sagging between her legs, forcing her to bend her knees from the diaper's sheer size. She was impressed out how well the garment held everything inside, as she slightly rocked herself back and forth, feeling the heavy diaper shift underneath her.

It was official: Twilight loved to soil herself. She loved to soil herself as much as her body and her diaper could manage, and she was confident this diaper could manage more. She wanted to push this diaper to its limit, to see how much it could take before its load started to spill out or the diaper snapped off her waist and spilled across the floor. She glanced back toward the spell she found as her horn lit up.

Studying could wait. She had an experiment to perform.

Author's Note

Thanks for reading! Feel free to suggest any future one-shots you would like to see, or if you'd like to see a follow-up to this one!