Sweetie Belle's Magical Mistake: Swapped Bodies and Soiled Diapers

by Eulshy

Rating: mature
Tags: My Little Pony: Friendship is Magic, Alternate Universe, Comedy, Rarity, Fetish, Spike, Random, Sweetie Belle, Twilight Sparkle
Length: 5997

Sweetie Belle is practicing magic with Twilight when she accidentally ends up swapping bodies with everypony in the room. (Involves AU headcanons and fetishy material)

While at Twilight's Library, Sweetie Belle is having difficulty practicing her magic when Rarity comes to pick her up, wanting one last chance to prove herself, Sweetie Belle attempts to cast her spell one more time only for it to go horribly wrong as she swaps the bodies of everypony in the room. How will the four of them come together to fix this, and will Sweetie Belle ever be allowed to practice magic again?

Published 2021-02-23 12:30:01 UTC
Last updated 2021-11-05 11:51:38 UTC

Chapter 1

The sun was just beginning to dip over the horizon as it cast it's brilliantly changing colors across the landscape of Ponyville. The vibrant colors of the evening sun bathed the surrounding area in a tranquil blanket of serene beauty as most creatures began to settle down for the night to come. The same somber calmness reached across a large tree house as it did with every other structure in the area, only to be shattered by the sound of light explosions and rattling objects as the occupants of said tree abode were long into a session on the merits of using magic correctly. The light that poured in from outside, like a caramel coating over the wood sculpted interior, was quickly cut aside as flashes of magic changed the lighting within. There in those ever changing lights stood three, two unicorns, a small white filly with lavender and pale pink locks, and a surprisingly white diaper, known as Sweetie Belle. The other, a lavender mare with mane of purple that had a pink streak through it by the name of Twilight Sparkle. Off to the side stood a small purple dragon adorned with green spines, and a slightly yellow stained diaper around his waist. All three of them looked to be generally exhausted, from any number of things that came with the rigors of training ones magical talent.

"I know we've been at this for some time Sweetie Belle, but I think you'll get the hang of it." Twilight stated.

Sweetie Belle's only response was to groan out loudly while stamping her hooves against the floor. Twilight looked around with a slight slump to her stance, looking at all the books that were strewn around and the overall mess that would need to be taken care of. While that was going on, a knocking came from the door to the library, to which Spike quickly waddled his way over to and opened it up, revealing none other that a white mare with an elegant purple mane.

"Oh hello Rarity!" Spike exclaimed excitedly as he held the door open, bowing his head slightly and waving his arm back in an elaborate manner to welcome Rarity inside.

"Thank you Spike." Rarity said as she came in. "I don't suppose the training has been going particularly well?" she continued after seeing the state of things.

Twilight shook her head. "Oh no, I feel like we've made some real progress today, Sweetie Belle was just trying out a spell to change the color of her mane." the mare explained.

"Well I suppose it'll have to sto-" Rarity was cut off by.

"No! I can do it! Please, just one more try before we go!" Sweetie Belle exclaimed with a high pitched whine.

"Sweetie Belle, I know you want to try to progress as quickly as possible, but sometimes you need to know when to call it a day. Besides, I'm sure Twilight would love to be finished so she can clean up and get a bit of rest." Rarity went on.

Sweetie Belle immediately found herself turned towards Twilight, eyes wide as she looked up at her mentor, of course it didn't take more than a moment for Twilight to wither under such a look.

"Oh it's fine Rarity, one more try couldn't possibly make this." Twilight gestured to the room with her hoof. "Any worse than it already is." she finished.

Rarity rolled her eyes for a moment. "Oh very well, but only one more try Sweetie Belle, we don't want to put off dinner any longer than we need to." Rarity stated

Sweetie Belle bounced in place as Spike went ahead and shut the door to the library, knowing better than to leave it open when Sweetie was about to try her magic. Spike headed back over to the far side of the room, as he passed Rarity, the mare scrunched her nose slightly at the scent of urine that she got a whiff of as he went by. Though before she managed to comment on it, her sister had gotten into a stance. Sweetie Belle was focused, she was ready. The filly began to charge herself up, magic building within her as she prepared to cast the spell. All eyes were on Sweetie Belle as the filly felt herself ready to try when something happened. Sweetie Belle could feel warm liquid splashing against her body, her diaper was growing heavy and wet as she urinated suddenly. A blush spread across her features, normally she wouldn't mind this at all, if it hadn't been for the fact that it was messing with her concentration and her sister was watching her. She was supposed to be using magic! Not wetting herself! Despite the lack of complete concentration, Sweetie Belle pushed ahead with the spell when things went wrong.

Rarity had been watching her sister intently as it seemed like Sweetie Belle had been building up to finally cast the spell, though she was immediately put off at the sight of her sisters diaper tinting a darker shade as liquid added to it and slowly the darker shade became a yellow discoloration. Rarity sighed as she realized Sweetie Belle was only going to accomplish making her diaper wet with all that exertion when the mare was suddenly blinded by an intense flash of light, and then she was out.

Twilight hadn't been paying much attention to Sweetie Belle as the filly did her best. Mainly she was thinking about getting Spike into a new diaper after this since she could see it from here and it looked heavy and swollen with how much urine it was currently holding, it was this lack of attention that caused her not to notice the sudden power surge Sweetie Belle had exuded. Completely caught off guard Twilight could do nothing to stop the blinding light from piecing her vision as she lost consciousness too.

Spike was just standing idly by, in case something happened where he'd need to move or perhaps move something out of the way, at the light from Sweetie's horn suddenly became intense, he realized something was about to happen, but he had little time to wonder that as he too felt his mind taking a back seat as he blacked out.

The sunlight that had bathed the place in a gentle glow was slowly dying away. Ambers and oranges began to fade into light reds and purples as the sun sank even lower into the horizon. Of all the creatures pass out on the floor, one began to stir. The dragon, it's limbs began to move spastically as it's eyes suddenly shot open and his cry pierced the still room. It was completely unintelligible, a mangled form of what could be considered language. In his flailing and gibbering, another form began to stir. Rarity. Picking herself off of the floor and into a seated position. The mare began to look around in confusion.

"What's go." was as far as the mare got before her voice seemed to just disappear.

'That's not my voice? No wait, isn't it? Why would my voice be, what voice?' thoughts raced within her mind as her eyes scanned the room

Rarity's eyes came to rest on the still form of her sister lying on the ground, the diaper that had been clean before was stained completely yellow by this point.

"Is that me?!" Rarity shouted.

It seemed to be true, Rarity was not the one looking down at her sister, but rather it was her sister who was looking down upon herself. Yes it seemed that somehow Sweetie Belle had put herself into her sister's body and vice versa. Sweetie Belle didn't feel much different. The only thing she could feel, was fatigue, but she assumed she would have felt tired now even in her own body! She had to do something, Twilight, she needed to get Twilight up too. Obviously something was wrong with Spike as well since the dragon seemed to be having some sort of fit on the floor. Getting to her hooves a bit unsteadily, Sweetie Belle slowly trotted over to Twilight, not used to being so far off the ground so suddenly, she reached the other unicorn and began to shake her.

"Twilight, you need to wake up! You have to fix this!" Sweetie Belle shouted.

The shouting and shaking seemed to do the trick, as Twilight began to stir as well, but she wasn't ready for the sudden hoof that came and hit her right in the jaw.

"Ow! What was that for!?" Sweetie Belle said, recoiling from such a hard hit.

But after she looked back over, she was horrified at what she saw. Twilight seemed to be flailing around on the floor, speaking gibberish and generally spazzing out. Much like Spike had been mere moments ago. Spike was now laying silently, Sweetie Belle had no idea what to do. She'd ruined everything and could feel the tears welling in her eyes.

"Rarity!" Spike suddenly shouted, grabbing Sweetie's attention.

"Spike?" Sweetie belle asked as she went over to the dragon on the floor.

Sweetie Belle looked down at the dragon, he seemed to be concentrating intensly as he laid there on the floor.

"Rarity. Not Spike. Twilight." was all Spike managed to get out.

Though it was all Sweetie Belle needed to hear in order to work things out.

"Twilight! I'm not Rarity, it's me, Sweetie, I'm in my sisters body!" Sweetie exclaimed.

Twilight looked somewhat perturbed by this, but it didn't stop her from continuing.

"Sweetie. Help. Need help." Twilight said.

"What do you want me to help you with?" Sweetie Belle asked her.

Twilight, in Spike's body, held up one claw and then pointed to her own body. "Help."

Sweetie went over to Twilight's body, which she could only assume was Spike, who had stopped convulsing and was just laying down now. Sweetie Belle righted the body, and laid it out on it's belly.

"Thanks." Spike said in Twilight's body, having gotten used to the change enough to speak properly.

Rarity got herself up and moved over closer to all of them as they were slowly getting used to things.
Twilight managed to sit herself up, wincing ever so slightly as she felt the sodden diaper squish against her scales. Realizing she was wearing Spike's wet diaper. Or technically, her wet diaper, in a way.

"Alright, so. Things have gotten a little out of control." Twilight spoke with Spike's voice, having gotten used to her body, it was a little odd hearing him speak in such a way, but that was hardly the strangest thing.

"A little!? Twilight our bodies have been switched, I don't know how this could be viewed as a 'little' problem!" Rarity exclaimed in Sweetie Belle's body, before bringing her rear down roughly onto the floor in a huff.. Completely forgetting she was in Sweetie's body, she felt her sister's sodden diaper squish warmly around her flank as her eyes went wide. "Eeuurgh!" she suddenly whined as she quickly jumped back up onto her hooves. "Oh this is disgusting!" Rarity exclaimed.

Sweetie Belle couldn't help but giggle at the situation, but said giggles soon earned her sister's attention.

"And what do you think is so funny! You are in so much trouble once we switch back Sweetie Belle!" Rarity shouted at her.

Sweetie Belle, despite being taller, felt herself withering under her sisters screams, her ears folding back as she turned her head away.

"Rarity!" Twilight exclaimed. "Fighting isn't going to solve anything right now. Not to mention if you continue to work yourself up like that you'll only cause yourself more headache for the moment." Twilight told her, being acutely aware of Sweetie Belle's body, she knew Sweetie Belle had a tendency to 'let loose' whenever she was nervous, or frustrated.

"Okay. Okay. Let's just all relax, and calm down." Rarity added, taking a deep breath and exhaling.

Twilight, Spike, and Sweetie Belle all decided to do it, mostly just to placate Rarity, each of them taking a deep breath, and sighing in turn, letting their bodies relax. Unfortunately, as Rarity let herself relax her tail subtly lifted up an inch, as a loud expulsion of air exited her rear end, making a horrifying spluttering sound as it echoed off of the inside of her wet diaper. Rarity's eyes went wide as she quickly assumed the worst, the other three also staring at her caused Rarity's face to light up like a bonfire before she quickly began to stare daggers at all of them as she realized, it was just gas, thankfully.

Sweetie Belle had been about to start giggling again when her sister's look changed, and although it was her face staring at her, she knew that look wouldn't mean good things for her if she let out even one little sound. Spike knew better than to say anything right now in regards to Rarity and was too busy trying to get himself upright, he'd managed to roll over onto his stomach at least, and Twilight quickly moved past it as she said.

"We need to get some things straight right now before we do anything else." Twilight said as she managed to sit herself up, feeling the wet diaper squishing around her scales, though the feeling wasn't terrible, not as terrible as she imagined it would be. "Those two, need diapers." Twilight continued while pointing to Rarity and Spike.

"What do you mean, they need diapers?" Rarity questioned.

"Well.. Spike and Sweetie Belle certainly aren't potty trained, and while they might have our bodies, they very likely won't recognize the right signals in order to.. Well, go to the bathroom." Twilight explained somewhat sheepishly, and once she'd finished explaining that, Rarity looked horrified.

"Absolutely not! I'm not going to have Sweetie Belle running about in my body wearing a diaper! Think of what everypony will say when they find out?" Rarity began to go on, only for Twilight to shout.

"Rarity!" Getting the mare's attention. "Would you rather that, or perhaps you'd enjoy hearing about the time you dropped a load of horseapples in the middle of Ponyville for the rest of your life after we've fixed this." Which was a statement that quickly ended Rarity's current complaints.. But not for long.

"Yes, but darling, how will we get them diapers? Perhaps we could slip Sweetie Belle's night diapers onto them, though they'd be stretched quite a bit by that." Rarity mentioned.

"I'm well aware, we'll likely need cloth diapers of some fashion." Twilight mentioned.

"Eugh.. It pains me to think of fabric being used for something so.. Filthy.. But I suppose if we got back to the boutique I might be able to do something.." Rarity said as she tried to light up Sweetie Belle's horn, finding it completely unresponsive. "Or.. Perhaps not.."

Twilight shook her head. "I doubt Sweetie Belle's body is going to be able to do any more magic for the rest of the day. Though that brings me to my next point. We need somepony else. As much as I would rather keep this under wraps, somepony is going to have to help us. Maybe Applejack or Fluttershy could work, but they're all the way on the other side of Ponyville.."

"Twilight you're not suggesting." Rarity began.

"Yes. We need to get Pinkie Pie.." Twilight finished.

"But who's going to go get her?" Rarity asked, internally dreading how much 'fun' Pinkie Pie was going to have with this situation.

"Oh! Oh! I can get her!" Sweetie Belle exclaimed as she bounced up and down, only to quickly be silenced by Rarity's loud.

"NO!- I mean, no, Sweetie Belle, you will stay right here."

"Yes, that is for the best. Rarity will have to go get her." Twilight stated.

"Why me?!" Rarity whined slightly as she turned her attention back to Twilight.

"Because Rarity, we can't let Sweetie Belle leave in case she has an 'accident' which would just get more ponies to notice her. Spike can barely move and I can hardly walk right now either." Twilight mentioned.

"Oh.. I suppose." Rarity said glumly as she got to her hooves, but before she could head away, Twilight called to her.

"Wait! You have to pretend to be Sweetie Belle until she gets here. Not that I'm entirely sure she'd believe you were you even if you told her, but I imagine you don't want to tell Pinkie then and there, since then everypony will know what happened." Twilight added.

To which Rarity nodded. "Right right. Wouldn't want anything like that happening." Rarity said as she began to trot off again. She could feel the wet diaper swaying slightly as she went, causing her to grimace slightly. Just as she reached the door another voice rang out.

"Wait!" This time it was Sweetie Belle. "Don't you want to get changed before you leave?"

Rarity frowned at the idea as she turned to face her sister. "As much as I don't enjoy sitting in your filth.. I was hoping to put off that little embarrassment for as long as possible." Rarity told her.

"But Pinkie Pie might try to change you if you show up in a wet diaper." Sweetie Belle mentioned.

A few moments passed as Rarity stood there, absorbing the information, before she asked. "Twilight, where do you keep Sweetie's diapers?" as she began trotting back towards them.

"On Spikes changing table." Twilight said.

"Sweetie come. You are going to clean up this mess you made, I will not be leaving until I am spotless." Rarity said as she trotted along past Sweetie Belle who just looked down at her sister with a sigh.

"Yes Rarity." Sweetie Belle said as she followed her sister upstairs.

Once the two of them had left, Spike looked to Twilight.

"So.. How do we fix this?" he asked, having managed to get his hooves under him now, but still laying on the floor.

Twilight sighed. "I'm not entirely sure, if I were in my own body I could begin casting some spells to see just what happened, but as we are, all I can do for the moment is hope that it's a temporary spell and it'll eventually wear off in a little while. Until I have somepony else we can rely on, that's going to be what we go with."

"Well, alright then." Spike said, and then continued. "Oh, and uh, sorry for when I eventually have an accident."

Twilight just shook her head. "Please Spike, it'll hardly be your fault at this point. Sweetie Belle might not know how to go, but at least she isn't working with a whole different species like you are." 'Not to mention different plumbing' Twilight thought to herself after her statement.

Meanwhile upstairs...

Sweetie Belle had picked up her sister and had laid her on the changing table, and unfortunately for Rarity, Sweetie Belle couldn't access her sister's magic, a few moments of sputtering and straining on Sweetie Belle's part had worried Rarity so much that she forbid her sister from trying to use magic while in her body. What was bad about that, was that Sweetie Belle would have to change the diaper, the old fashioned way.

Laying there as her diaper was untaped, feeling the cool air rush against her warmed fur, Rarity couldn't help but shudder as she knew she was going to be scrubbing her mouth out for days once this was all over as she watched Sweetie Belle pulling the wet diaper out between her teeth.

For the most part Sweetie Belle had thought this was going to be a neat experience, she'd never changed her sisters diapers before! Since her sister didn't wear them obviously, but it quickly turned into a sour experience as she caught the taste of her own urine as she grabbed the diaper in her mouth, tossing it in the nearby diaper pail as quick as she could, she got to wiping Rarity down. Thankfully the taste of the foal wipe took the taste of pee out of her mouth, but unfortunately, now she tasted foal wipe. It was rather awkward for her as she dragged her head across her Rarity's crotch and hind legs. Which in reality was her own body, which was odd to see from this angle to be sure, let along cleaning it!

Likewise it was just as awkward for Rarity, who wanted to not say anything during the change, but constantly found herself going. "You have to wipe inside a bit further Sweetie Belle, otherwise it's a health risk." or "Make sure you clean the fur properly, there should be no yellow stains! They show up really easily on your coat, goodness I think I'll need a bath though." What did end Rarity's rambling was when Sweetie Belle pushed the wipe into the filly's butthole, just a little, to make sure she was clean there, even though the diaper was only wet. A small shrill noise was the last thing Rarity uttered before Sweetie Belle moved on to sprinkling foal powder across Rarity's flank. After which she grabbed the new diaper, unfolded it, set Rarity into it, made sure to thread the tail through the back hole properly, then set about folding it up.

"Alright! Done." Sweetie Belle said as Rarity turned over and stood up on the table.

Rarity wiggled her flank and stretched her hind hooves. "I suppose you've done a good job here Sweetie Belle, it's fitting correctly, not too tight or too loose anywhere." Rarity commented as she hopped down from the changing table. "Now, I shall make my way to Sugarcube Corner. Hopefully once I bring Pinkie Pie here, we can get to work on getting this all situated."

Rarity and Sweetie Belle went back downstairs, where Twilight had managed to stand, somewhat shakily, while Spike had forgone trying to walk properly and was just crawling about, or shimmying himself along.

"So long Twilight, I shall be back as soon as possible." Rarity mentioned as she trotted to the door, opening it, and left, shutting the door behind her.

Spike and Sweetie Belle both looked at Twilight, whom found it odd to be staring at her own face as Spike looked at her. "Now, you two are going to the bathroom. Sweetie Belle you're going to sit on the toilet until Rarity gets back. Spike is getting in the tub."

Both of them looked annoyed, but offered no argument as Sweetie Belle attempted to help Spike get to the bathroom. As they went, Twilight idly rubbed the front of her diaper, feeling it squish wetly. She knew she was risking a diaper rash by not having Sweetie Belle change her, but she figured she could wait until Pinkie Pie got here, Twilight would deal with it, if it meant not risking watching Rarity defecate on the floor. A thought that made her shake her head as she unsteadily waddled after the two of them.

Chapter 2

Rarity trotted her way down the streets of Ponyville, she'd done this plenty of times before, but this was the first time she was seeing it from this angle, not to mention the constantly crinkling at her every step, was more than a 'little' annoying to her, but she kept moving. Despite constantly thinking every pony was looking at her, no pony was, there were no second glances at the filly trotting down the street in a diaper, it wasn't unusual or out of the ordinary, for Rarity it sure was, but no one knew it was her, they only saw Sweetie Belle, and despite knowing that was the case, Rarity still couldn't help but feel somewhat jittery as she made her way towards Sugar cube Corner.

There were a lot of positives going for her right now, it was later in the day, which meant not as many customers around, Sugar cube Corner saw much more activity during the morning to late afternoon, as it approached the early evening, most ponies stopping in were likely getting something for desert at home later. As long as nothing went awry, this should be a very simply task. Once she got to the front door of the establishment, Rarity took a deep breath, and exhaled.

"Okay Rarity, just go in there, tell Pinkie Pie that Twilight needs her, now, and escort her back. Simple, easy."

That's what she told herself right before heading inside. Like she thought, the place was fairly empty, a few ponies were seated, enjoying confectioneries, but there were two ponies there she was not looking forwards to seeing. Apple Bloom and Scootaloo. Before she could scamper away, the two fillies noticed her and waved her down.

"Sweetie Belle, there you are, we've been waitin' here ferever for you to show up."

Apple Bloom's voice cut across the room as clear as day, Rarity wanted to ignore them, but she couldn't, not because it would be weird or anything, but because those two would end up doing 'something' to bring far too much attention to her. So altering her plans, she went towards the table those two were seated at. All she had to do was explain she was busy, and then continue with her task. As she got to the table, she hopped into one of the chairs, only to immediately be met with a cupcake to the face.

"Here Sweetie Belle, we've been saving this one for you."

Scootaloo said while pushing the cupcake into Sweetie Belle's mouth, forcing Rarity to start eating and swallowing the admittedly delicious pastry. After quickly eating it, she coughed a little.

"Look at what you did Scootaloo, here, drink some of this."

And before Rarity could even contemplate Apple Bloom's words, a bottle of soda had been forced into her mouth, she began swallowing the sweet cola, if only to stop herself from choking on it, drinking the bottle until it was completely emptied, once it was, it was pulled out of her mouth, leaving her feeling slightly dazed, and a little nauseous. A full feeling in her stomach after downing both the cupcake and the drink, though that feeling soon began to rise as her eyes widened and before she could even attempt to stop it a booming.

"URRrrulp!"

Echoed out of her mouth. Both the other fillies began to giggle as they said.

"Nice one!"

In unison. After that transpired, and Rarity had hold of her senses and wasn't being force fed, she picked up a nearby napkin and began to wipe the bits of frosting stuck to her muzzle.

"Huh, is Rarity rubbing off on you Sweetie Belle? I've never seen you use a napkin to wipe your face before."

Scootaloo commented, and before Rarity could say otherwise, Apple Bloom spoke up.

"After that belch? I reckon Rarity might have fainted if she'd heard that."

Which made Rarity narrow her eyes a little, but she quickly got over it, she wasn't here for this, she needed Pinkie Pie!

"Girls please, I know you were uh, waiting for me, but I have something quite impor-"

Rarity find herself losing her voice as the rather delightful smell of the bakery was suddenly cut off and replaced with that oh so familiar scent of fresh horse apples. She couldn't help it as she suddenly gagged. A moment after that, Scootaloo raised her hooves over her nose.

"Oh jeez Apple Bloom, how long were you holding that in!"

The Pegasus filly began flapping her wings to mitigate the stench as Apple Bloom had a sheepish smile on her face.

"Well it's been a while since I last ate, and I weren't holdin' nothing, it just happened to come out now is all. Sides, I don't know what y'all are complaining about, I've smelt your dirty diapers too, and they aren't any better."

Rarity finally regained her composure, doing her best to cover her nose with her hoof, she was actually breathing heavily to block the scent of filly manure with her breath, which smelled of cupcakes and was much preferable.

"Girls!"

Rarity exclaimed, getting there attention once more.

"Like I was trying to say, Twilight needed me to do something really important as part of my magic training, which is why I was late, and which is why I can't stay, she needs me to get Pinkie Pie for her."

Both the other fillies looked at her for a moment, seemingly onto the fact that things weren't quite what they seemed.

"Okay. See yah tomorrow Sweetie Belle."

Scootaloo said as she hopped off her chair.

"Bye Sweetie! Hope your magic stuff goes alright."

Apple Bloom added as she hopped off too. Rarity watched the two of them head out the door, her eyes fixated on Apple Blooms full diaper as it swayed back and forth as the filly trotted out. Taking her hoof away from her face as the scent of dirty diaper quickly dissipated, and the scent of baked goods reigned supreme once more.

"Thank goodness, now to get Pinkie PIE!"

Rarity had turned her head back around as she said that, finding Pinkie Pie directly in front of her, scaring her right off of her chair and onto the floor.

"I heard you were looking for me!"

Pinkie Pie stated, with a level of enthusiasm that only Pinkie Pie could constantly bring to the table, Rarity didn't even bother thinking about how Pinkie Pie had known she was here for her, it just saved her the trouble of finding her at the very least, picking herself up off the floor, Rarity shook herself for a moment and looked up to Pinkie Pie.

"Pinkie Pie, I'm here tough!"

Rarity yelped out in disgust as she suddenly felt the party pony's tongue slide against the side of her face.

"You had a little frosting stuck there, don't worry, I took care of it."

Pinkie Pie said as she smiled down at Rarity, who just fumed inwardly at the situation as it transpired, only keeping her cool knowing that Sweetie Belle wouldn't be upset by that, so she had to maintain her composure. Though after her sudden snack just a few moments ago, she was feeling a lot less confident with herself, in fact, she was feeling a little uncomfortable, but she brushed the feeling aside as she began to speak again.

"Pinkie Pie, I'm here because-"

"You need a diaper change?"

Pinkie Pie said as she was suddenly behind Rarity, hoof pressing against the back of her diaper, feeling it poking her flank.

"Oh wait your clean, I could have sworn-"

Pinkie began, only for Rarity to interrupt her this time.

"Pinkie Pie!"

Rarity stamped her fore hooves onto the floor for emphasis.

"I do not need a diaper change! If you're smelling a dirty diaper, that's because Apple Bloom just left and took hers with her."

Rarity said, feeling the need to clarify her diaper was spotless.

"Now, I'm here, because Twilight said she needed you to come over right away!"

Rarity shouted out.

"Oh, okay!"

Pinkie Pie replied in turn, still standing behind Rarity, who let out an exasperated sigh at finally getting Pinkie to listen to her, she could feel herself relax as she knew all she had to do now was get Pinkie Pie back to Twilight's. That's when disaster struck. The feeling of relief washed over Rarity in more ways than one as her tail hiked up, a sudden twisting knot formed in the pit of her stomach as Rarity instantly recognized the feeling.

"No, no, no!"

The mare pleaded to herself as she desperately tried to force her sister's body to clamp down tightly on the feeling inside of her, but after a few mere seconds of holding it in, the knot began to slide undone and Rarity felt a mixture of blissful relief and pure disgust wash over her as her fore hooves shook for a moment before lowering slightly, raising her rear end sky-high as her bowels began to empty. It was like a faucet had been turned inside her body, one she had no means of stopping as a sloppy muck began to empty out of her backside, landing right into the waiting diaper. The smell of her shame spread around her, fighting off the delectable scent of delicious backed goods and replacing it with the murky mire of manure, feeling the diaper tugging downwards as it filled slowly over the course of the next minute, though it seemed like an eternity to Rarity as she could do nothing but feel the waves of pressure sliding more horrifying sludge out of her, until it stopped.

Rarity began to breath heavily, taking rapid breaths, as if she hadn't breathed at all while soiling herself. Before she could even begin to come to terms with what had just occurred, she felt herself being lifted around the belly.

"Well, I better take care of this quick before I go, I know how much Rarity hates changing poopy diapers!"

Pinkie Pie exclaimed as Rarity felt her face heat up as every pony else was made aware of the accident in her foal pants. There was nothing she could do to get out of this situation, even if she didn't have Pinkie Pie dragging her to a changing table right now, it wasn't like she wanted to stay in this filthy thing! Of course, ever fiber of her being had wanted to avoid this particular part of being her sister, but it had happened, and so suddenly too, it just hadn't given her enough time to process the whole ordeal, and before she knew it, she was in the Cake's nursery, being laid upon the changing table, a table where foals had their diapers changed. Rarity simply stared up at the ceiling as the sounds of the diaper tapes being pulled back could be heard. She didn't even wan to look at Pinkie Pie, knowing how the Earth pony would be handling the diaper change made bile rise up in the back of her throat.

"Whew! What has Rarity been feeding you!"

Rarity heard the comment and wanted to simply vanish from existence. The thought of thinking of the food she'd made before leading to this, it had her mind reeling, she was trying to distance herself from the whole situation, but Pinkie Pie had brought her right back to it with one innocuous statement. Soon the diaper was pulled out, she felt it slide against her body as Pinkie Pie used it to scoop up most of her waste. Then came the wipes, the coolness was Rarity's saving grace, she was being cleaned up, it was demeaning, embarrassing, but it was coming to an end.

Rarity found herself enjoying the feeling of the muck getting wiped off of her, which caused her concern at first, but she shook her head. She was getting clean, of course she would enjoy that. Although as the scent of foal powder joined the mix, Rarity quietly sighed to herself, the smell hadn't gotten overly better, now it simply smelled like Sweetie Belle's room as opposed to just smelling of soiled diaper. With the powder applied, her flank was lifted, a new diaper slid under and her tail tucked into the hole. It was taped up and Rarity found herself on Pinkie Pie's back. All in all, that had only taken a fraction of the time it took Rarity to change her sister, and Pinkie Pie didn't have any magic! Which just showed how much Rarity despised the task in general. But that was soon getting pushed to the back of her mind, all of it was.

"Twilight needs me! Be back later!"

Were the last things Rarity heard before she headed back out, with Pinkie Pie carrying her, at least her mission had been successful, for certain definitions of success anyway.