[Fanfic] K-ON! Diaper Days: Yui and Ui

Based off of the second part of the doujin K-ON! Diaper Days. This story has much the same problems as the Mio and Ritsu story in that it’s kind of heavily introspective (some people like that but I think this is a bit extreme). Even though I could see Ui, the perspective character, doing this much thinking, I decided to try to dumb down her wordings a bit so that it would sound like it could realistically come from her character… but then I forgot I was doing that really fast and just kind of wrote how I usually do. Oh well, at least it’s legible.


K-ON! Diaper Days

Yui and Ui

“Ui!” a very familiar voice, with a very familiar tone, rang throughout the house.

The intended target of said call could already tell just by the way her big sister said her name what she would be faced with once she responded. She paused from her preparation of the vegetables for their dinner and set down the knife before preemptively grabbing a roll of paper towels, some rubber gloves, and a spray bottle of cleaning solution. This had happened often enough lately that she now kept all these things within reach on the kitchen counter at all times.

Even though she knew what was coming, she went ahead and asked like always. “What is it, big sis?”

“I peed.” The reply came almost instantly. And it was exactly what Ui expected to hear.

“Okay, I’m on my way.”

With a sigh, the younger Hirasawa left the kitchen and made her way to the living room. When she arrived, she found her sister sitting at the coffee table, staring at the television, which was apparently on and showing some magical girl anime at a low volume. On the wooden floor beneath her sitting form was a puddle of golden liquid – urine.

“Stand up, sis,” Ui requested, her inner distress fortunately not showing up in her voice. “I need to clean it before it soaks in.”

The older sibling stood up and walked to the side a bit, a few drops of pee falling from the back of her shorts onto the floor, creating a bit more mess to clean. Ui walked up to the coffee table and set the spray bottle and paper towels down on it before donning the rubber gloves. Next, she walked over to the side of the room and grabbed the small trash can, bringing it over and setting it down close by for later use. She then picked up the roll of white paper back up and tore a few rectangles off before folding them up to layer them.

As she sat down, the younger sibling began wiping the main puddle of pee up with the paper towels in a circular motion. After she got the bulk of it, she discarded the yellowed paper in the trash can. She then tore off a fresh few of the white sheets, layered them, and repeated the wiping process on the places that got dripped on by Yui’s shorts, which had thankfully stopped by that point. The older sister herself moved a little further off to the side so her feet didn’t interfere with the process.

After discarding the second layer of paper towels in the trash can, she grabbed the spray bottle and sprayed some cleaning solution onto the floor. She allowed herself to think about what happened while giving the cleaning solution time to do its thing.

Even a month ago, she wouldn’t have imagined that this sort of thing would ever happen, much less that it would occur regularly. But at this point, she had become desensitized to it, seeing as it had happened at least a few dozen times. It started about three weeks prior. While Ui was making their dinner, she heard her sister call out to her in a tone that was kind of similar to the one she used when she spilled something, but kind of distinct from it, too. She asked what happened, to which she got the same response that she did every subsequent time: just “I peed.”

At first it only happened once every few days. But then, it started getting more frequent, until it was happening every day at around dinner time. That was already bad enough on its own, but after the second week, Ui started noticing an unusual increase in her sister’s underwear to wash. She eventually figured out that her older sister was changing panties after she got home from school and putting the old ones in the laundry. And even the ones she only wore at school had small pee stains on them more often than not. Which meant that she was not only having accidents at home, but also at school.

It was becoming a real big problem. Ui would do anything for her big sis, but at the same time, she didn’t really like the increase in laundry and having to clean up every time this happened. It took her two weeks of dealing with it before she forced herself to make a rather… heavy decision. She needed to cut down on the constant cleaning, so she bought some things on the internet in order to help her. They came in the mail just that morning, and she told herself that she would introduce the concept to her sister the next time she had an accident.

Well, this was that time. As she tore off the final few paper towels and used them to wipe up the cleaning solution, the younger Hirasawa spoke, turning her head to get a better look at her sister’s reaction. “Big sis, you’ve been wetting yourself a lot lately. Why don’t you try wearing diapers for a while until it gets better?”

This was the decision she had to make. If Yui was going to wet herself all the time, she’d need to do something to prevent the laundry from piling up so much and keep her younger sister from having to clean up the puddles. Namely, she’d have to wear protection to keep the pee from making a mess everywhere, or to put it bluntly, diapers.

When the younger sister suggested it, she expected there to be at least a little resistance. After all, being put back in diapers was typically seen as humiliating. Ui was prepared to bring up a plethora of… statistics, for lack of a better word, like how many times she’d had an accident in the past few weeks, or how many extra pairs of panties, never mind the other articles of clothing, had to be washed because of them. Well, the reaction she actually got was a whole lot more anticlimactic than what she anticipated.

“Okay,” Yui agreed right away with a nod of her head. “If you say so, Ui, that will be fine.”

The immediate acceptance took the wind out of her sails, so to speak. When words failed her, the younger sister merely nodded, got up, and walked over to the closet in the hallway, which was where she unpacked the diapers that arrived in the mail. She opened the door and grabbed the things she needed – she decided to buy standard Japanese adult-sized cloth diapers for the time being, so that meant getting a cover and the diaper itself, which was a very long sheet of white, absorbent cloth that could be layered to the desired specifications.

As she brought them back over to the coffee table, she found something to say. “You can’t tell the other members of the light music club about this unless they figure it out themselves, okay?”

“Got it,” the older sister replied, face almost unreadably blank. “It’s embarrassing, so talking about it would be hard anyway.”

“Good, now take off your shorts and underwear and lie down for me,” Ui commanded gently. “We’ll put it on you now so you can get used to the feeling.”

Yui nodded her head and did as she was told, pulling all the clothes on her lower body off and setting them down a little ways away. Fortunately, the wet parts weren’t touching the floor, so the younger sister wouldn’t have to break out the cleaning supplies if she acted fast enough. As the older sister lay down on the ground, Ui layered up the cloth diaper and opened up the Velcro waterproof cover before setting the padding inside it.

“Behind up, please.”

Her sister once again did as instructed, bending her knees and lifting her bare rear end into the air. The younger Hirasawa promptly slid the newly-prepared diaper under her and centered it perfectly. Yui lowered herself back onto it the moment her hands moved out from under the area.

“It’s really soft,” was her only commentary.

Since the older sibling had just wet herself, Ui decided to wipe her behind with the cleaning wipes. She made sure to be extra thorough, since she didn’t know how long she had been sitting in the puddle of pee before she noticed and called out. Once done, she tossed the wipes in the trash can and began pulling the diaper up.

“Also, when you have gym class, you should wear regular underwear,” the younger Hirasawa added as she pulled the layered cloth over her sister’s privates. “If you wore a diaper, everyone would be surprised in the locker room, huh?”


Ui pulled up the front of the cover, making sure it was snug enough to prevent leaks, but loose enough to not be painful. Then she pulled up the sides of the diaper and fastened the Velcro patches, one at a time. While admiring her handiwork, a thought occurred to her: though she had made sure to layer it extra thick, any kind of diaper would probably not last the entire school day. Which meant that Yui would need to be changed at once during school if she wet herself enough.

As she stood up and helped her sister to her feet, she decided to say something about it. “If you need to be changed at school, or you think you should be put back in a diaper after gym class is over, ask the teacher to go to the bathroom and text me once you get there. I’ll be sure to pack spare diapers in my bag so I can change you.”

“Got it,” Yui affirmed with a nod.

“Okay, we’re all done here. Remember, if you notice that you have to pee, you can take it off and go to the toilet, then come get me to either put it back on or change you into a new one,” the younger sister concluded, going and picking up the soiled underwear and shorts. “Now, it’s time to go put these in the wash and get back to working on dinner.”

That day marked the first of countless diaper changes for Yui Hirasawa.


A small, short vibration on her thigh, accompanied by a characteristic buzzing sound, tore Ui’s attention away from her classwork. She looked up at the clock before getting her phone, and sure enough, it was about the usual time.

Just to make sure, she grabbed her cell phone from its spot inside her pocket and flipped it open. As she expected, she had one new text from her sister. She opened it up, and as per the usual for this time of this day of the week, it just said one short request.

“Gym class is over now, can you come change me?”

Today was a gym day for the lead guitarist of the light music club. As per the usual, as soon as it ended, she must have sent a text, asking to be changed into a fresh diaper. Ui found it a little weird that her sis would so willingly give up her big girl underwear like that, but she soon grew used to it, since it happened every single time.

She discreetly texted out a quick reply, saying she’d be there soon. Right after putting her phone away, she grabbed her bag from its spot next to her desk, walked up to the teacher, and quietly asked to use the restroom. She got a reminder that class would be over soon, but ultimately, she was allowed to leave, and the teacher said he’d let the next instructor know she would be out for a little while. As she walked out into the hallway, her mind fell into its usual thought pattern during times like these.

It had been around two months since Yui started wearing diapers to contain her wetting accidents, which didn’t seem to be stopping anytime soon. In fact, rather than get better, they only got worse with time. Before she started wearing protection, she only wet herself once or twice a day, but otherwise seemed to go to the toilet.

But after just a few days of diapers, Yui stopped peeing in the bathroom entirely. She apparently must have decided that just going in her padding was more convenient… or something, Ui honestly couldn’t tell what she was thinking. Every time she had to pee, she let it out right into her new personal toilet right then and there. The younger sister had even witnessed it happening multiple times – she always stopped moving when the flow started and didn’t resume what she was doing until finished, but otherwise, it was actually really hard to tell it happened.

But gradually, even that sign faded away as she grew more accustomed to wetting wherever and whenever she felt the urge, even while moving. Ui suspected that her sis just stopped holding her bladder entirely, keeping it relaxed and ready to release at all times. She couldn’t tell whether this was on purpose or not for the first couple weeks, actually. But shortly after the one month mark, it started becoming very apparent that Yui was wetting herself without even noticing.

And not noticing it meant that she just kept on doing whatever she was doing before, completely unaware of the state of her diaper unless it was just about to leak. This, of course, meant that every once in a while, if possible, her younger sister had to check to see if she needed a change. More often than not, she actually did, even when she herself commented that she didn’t recall when she peed.

Since Yui hadn’t specified a bathroom in her text, this meant that she must have been at the place she usually went to get changed: the nurse’s office. Around the time Ui realized diapers were likely going to be permanent, or at least long-term, in her sister’s life, she decided to let the school nurse in on it to make things more convenient. After all, the infirmary had its own personal bathroom with a locking door, which made ensuring the changing process happened in private much, much easier.

In addition, this also enabled the younger sister to keep spare diapers at school without taking up space in her bag and running the risk of someone looking inside and seeing them. She just kept them in a plastic box with a lid, stored in the cabinet below the private bathroom’s sink. In order to avoid confusing which box was which, since there were others in there, Yui’s first name was written on her box.

While Ui never made a habit of snooping around in other people’s boxes, she couldn’t help but notice that, starting about a week ago, a new box appeared in the cabinet… one that had the first name of the light music club’s bassist: Mio. And she’d seen it half open once while getting Yui’s box out, which showed her a tiny peek of a familiar multicolored star print on a white background. One she knew all too well because it was one of the standard prints for the brand of diaper covers her sister wore.

Naturally, she didn’t say a word about this to anyone. It wasn’t her business, so even if she was a little curious about it, she knew she shouldn’t pursue it. After all, she knew she wouldn’t like it if someone her big sis wearing a diaper and just went up and asked one of the siblings about it, or even worse, went talking about it to other people. Plus, Mio could have had a far worse reaction to wearing diapers than Yui did. She might not want to talk about it if suddenly confronted.

Ui arrived at the nurse’s office in what seemed like no time at all. It was actually quite the long walk from her classroom to the infirmary, but she never really noticed it, since she always got lost in thought on the way. She always thought on the same track during the trek: things like how long Yui had been in diapers for, how much worse her accidents had gotten, and other, similar matters.

The second year Hirasawa opened the door to the infirmary and stepped inside. The layout of the room was pretty simple: on the left side, a bunch of beds were lined up against the wall, from the exit to the windows on the other side of the room. On the right, the bathroom took up some space right as you came in, but beyond that, there was an examination area, as well as the nurse’s desk space right by the window.

Said nurse currently resided in the room, at her desk, but other than her, the place appeared to be vacant – nobody was laying down in any of the beds, and there wasn’t anybody in the examination area, either. She was a fairly thin, young looking woman with bright blonde hair, pale white skin and clear blue eyes, all of which she claimed were pretty normal in the European country she was born in.

Those eyes took notice of Ui the moment she stepped inside. “Ui-chan, welcome back! Your sister went into the restroom to wait. She told me she’d leave the door unlocked so you could go right in.”

“Thank you, ma’am,” the second year replied as she turned towards the bathroom, trying to keep her inner negativity undetectable in her voice.

It was an odd feeling when the nurse said ‘welcome back’ because she came there to change her sister’s wet diapers so often – always at least once a day, sometimes twice. It was kind of depressing, to say the least. She’d probably be a lot more upset about it if Yui actually seemed to mind wearing and using the adult-sized yet infantile garments. But she seemed to be perfectly fine with it… she could possibly have even preferred it that way, considering how quickly she fell down the rabbit hole of incontinence. When her diapers were concerned, the third year always seemed to suddenly become ten times more unreadable than her normal airheaded attitude. It made it incredibly difficult to gauge how she really felt about everything happening to her.

“Hey, Ui-chan? Before you go in…” she trailed off, waiting until Ui turned her head over to look at her. “The school year is going to end soon. Don’t you think you should teach her to change herself before she goes off to college? You won’t be able to do it for her when you’re in different schools.”

The second year nodded her head in acknowledgement. “Yes, I do plan to teach her how before the school year ends.”

“Okay, then. Good luck!”

It was a problem she’d thought of, but not actually set about to fix yet. Once Yui was off in college, she’d be on her own in regards to diaper changes for at least a year. The younger sister still had one year of high school left, after all. While she was confident she could teach her big sis to change herself, that wasn’t exactly the problem.

The issue was that the third year tended to not notice she needed to change until she was just about to leak. Even if she could do it herself, there was no guarantee that she’d manage to stay on top of diaper changes. Ui figured that probably came with the territory of wetting herself without noticing.

The frustrated second year ran a hand through her hair before grabbing the handle to the bathroom door and turning it. She pushed the door open just enough to slip through, then shut it behind her.

The infirmary’s private bathroom was pretty spacious, especially for all that it had in it. On the far right, the sink and supply cabinet were built into the walls at the corner. To the left of that, there was a toilet, and to its left, a small shower stall with a sliding door. In between the toilet and the sink was a small trash can with a revolving lid you could just push on to put things in. But all this, sans the shower, only took up a major portion of one wall. Around half of the white tile flooring was open space, not taken up by anything. Because of this, usually, they did diaper changes on the floor, though not without a changing mat.

Yui herself happened to be sitting on the toilet (which thankfully had both lids down). She noticed Ui enter – she was looking right at her – but she didn’t say anything. As usual for things involving her diapers, she seemed detached.

“Let’s get started, sis,” the second year said as she went over to the cabinet and opened it, grabbing Yui’s box from inside and setting it on the sink counter. Right after closing the door for the time being, she set her bag down against it on the tile flooring. “Have you made sure you’re all empty already?”

“Yeah, right before I texted you.”

When she said ‘all empty’, Ui was referring to both pee and the other. There had been several times where Yui forgot to go… number two between diaper changes until the need became urgent, which almost resulted in solid accidents more than once. Thankfully, none had actually happened as of yet, so the guitarist at least still seemed to have control over her bowels… for the time being, at the very least.

The second year got out the supplies one by one and set them on the floor. A bottle of wipes, some baby powder in a navy-blue container, the cloth diaper, the pale pink-colored waterproof cover, and finally, a changing mat, which she spread out on the floor behind her. Her sister came over and lied down on the mat without having to be told, having been through this at least a hundred times.

Ui pulled the guitarist’s skirt out of the way, revealing her white underwear… which was actually quite wet. There was a very noticeable yellow spot in the center. This immediately made the younger sister suspect that there was also a pee stain on Yui’s gym shorts. The fact that it only seemed to be in the center, though, suggested that rather than being from one big accident, the spot came from small leakage over a long period of time.

“You’re pretty wet, sis,” she commented as she removed the still-damp underwear, leaving her sister’s lower region bare. “Did you not notice? And did it get on your gym shorts?”

“It did get on my shorts a little, but you had to be looking from below to see it, so nobody noticed,” Yui replied in a fairly blank voice. “I never noticed until right after it had already come out. I’m used to not holding it in since I wear diapers, so I have to concentrate really hard to keep myself from just letting go. And I can’t keep it up for very long.”

That was about what Ui expected, but it was still a little disheartening to hear. She was beginning to wonder if putting her in panties for gym was really a good idea. Which was more obvious, a diaper bulge or a wet spot on one’s gym shorts? At the very least, the school year was almost over, with just a few weeks left. And come college in April, Yui would be able to wear whatever she wanted, both in class and in gym. Which meant she could wear clothes that more easily concealed the bulk of a diaper.

This, of course, also meant that she would stop wearing panties entirely. Since by that point, she only wore them for a few hours on gym days anyway, and wore diapers the rest of the time. And even that clearly wasn’t working out very well anymore – these accidents during the few hours she would wear panties every week were becoming a regular thing. It was only a matter of time before one was big enough that other people would notice it.

Ui had been preparing the diaper while thinking, so when her sister raised her behind right before she would have been asked, she slid the garment under her and centered it. After Yui lowered herself back onto it, the younger sibling took a few wipes from the container next to them and began cleaning up the guitarist’s privates. Once she finished with that, she tossed the wipes into the trash can and moved onto the next step.

Namely, she grabbed and opened the container of baby powder and sprinkled a liberal amount onto her sister’s privates. She rubbed it in gently, making sure she didn’t miss any areas so as to better prevent rashes. After that was over, she closed the lid on the container and set it aside.

“Sis, you wearing panties to gym class doesn’t work very well for hiding your problem if you wet yourself anyway,” she said as she began to pull the thickly-layered cloth up over her sister’s powdered privates. “Do you want me to see if I can get you a health exception to gym class so that you can sit on the side, not have to change into your gym clothes and wear diapers to keep people from seeing you wetting yourself?”

“Whatever makes it easier on you,” Yui replied, her voice once again hard to read. “You’re the one who changes me and does the laundry, after all. Gym is kind of hard anyway since leaking into my panties so often makes it hard to concentrate.”

With the decision put in her hands, Ui merely nodded her head as she brought up the front of the diaper cover. “I’ll see if I can get you that exception.”

Her older sister’s wording reminded her of how she needed to be taught to change herself before college started. She’d probably do it, along with teaching her to be more mindful of her diaper’s state, around the time school ended. She had another few weeks to put of what she was sure would be a massive challenge.

After fastening the Velcro on the pale pink diaper cover, Ui started picking up the supplies, as well as Yui’s wet panties. She then stood up, putting them in Yui’s box, including the underwear (though it got sealed in a plastic bag first for sanitary reasons), then taking it from the counter and opening up the cabinet below. As she set it back in its normal place at around the same time her big sis stood back up and smoothed out her skirt, the second year saw a familiar box a few centimeters to the right, and with it, an idea came to her. But she quickly dismissed it as soon as she thought about the logistics.

She had considered, for a second, asking Mio to change her sis while they were in college. But then she realized that in order to do that, she’d have to let the bassist know that she knew they both wore diapers. Which would of course be a huge invasion of privacy, not to mention possibly very insensitive. She clearly couldn’t do that to the poor raven-haired girl.

“We’re done,” Ui said, grabbing her bag before walking over to the door and opening it, belatedly realizing she never locked it. Her sister followed suit, and after some parting greetings to the nurse, they left the infirmary together.

Before they started using the nurse’s office, Ui would have taken the wet panties home to put them in the laundry. But the school nurse was a nice woman in a lot of ways, and liked to make things easier on the kids. So she always took any dirty clothes left in her office home and washed them herself before bringing them back the next day. This, of course, included the used panties and diapers left in her private restroom, too.

It was really convenient for the younger Hirasawa, who otherwise would have to wash those things herself. While it was a bit embarrassing, she was definitely glad that the nurse was willing to go above and beyond her job description to make the students’ lives easier.

When the siblings had to split up to go to their own classes, the first thing that the younger sister thought of once alone was how she’d probably have to change Yui again near the end of the day. She mused it was probably weird to be thinking about changing an older teen’s diaper at all, but it’s not like she could help it in this scenario.

This had become the new norm for the Hirasawa siblings. And the way things were going, it looked like diapers would be a part of the older sister’s life for a very long time to come.


There is a continuation of the two short stories I just posted, but it’s an unfinished multi-chapter story. I think I’ll wait on posting it until I’ve gotten some comments/critiques on these ones, just to check for interest in both the work and my writing style. Please be aware that both of the pieces I just posted are about three months old, so my writing style has changed slightly since then. I’ll post some of my newer works when I have some to show that aren’t from my Love Live AUverse.

Re: [Fanfic] K-ON! Diaper Days: Yui and Ui

I liked it.

It’s an interesting perspective; one that’s a little less common. Letting us see the thoughts of the caregiver, but not the ‘diapered’ allows me to relate to Ui a little; sharing her confusion at the rapid loss of control that her sister is experiencing.

I’m not going to bash the lack of explanation on that, (since you mentioned it in the footnotes of the other story) for a few reasons. A couple of them being that I’ve not read or watched any of the source material. Since I googled “K-ON Diaper Days” and found other stories, and without really researching them any more than that, I’m not even sure if I know the entire scope of the source material. Lastly, were you to continue this story, with the focus being on Ui, I could see it being an interesting read, even without a full reveal for the cause of Yui’s sudden incontinence. “Something something about it’s the ride, not where you’re going…”

Anyway, that said, I do find that I’m lost on a couple things. Sadly, as mentioned above, I have no investment in the source material, and thus am a little lacking on the context of the characters. Had I watched or read any of it, I’d at least know what everyone looked like, their general mannerisms (apart from what I picked up in your story), and what the hell any of this has to do with playing instruments. :stuck_out_tongue: Again, I feel that I don’t really have any ground to bash calling someone a bassist or guitarist, without having read anything that explains just that. But it still seems a little out of place to use such descriptions if nothing to do with the music club is actually part of this story.

So that’s basically a longer way of saying. "I like it, it’s good; but I don’t know what ‘K-ON’ is and don’t plan to look into it.
If there’s a way to say that without coming across as a dick, I’m hoping it involves leaving a disclaimer like this, followed by a smiley. :wink:

Re: [Fanfic] K-ON! Diaper Days: Yui and Ui

Here’s a link to the doujin that these two one-shots were based off of: Redirect

Actually, the other stories you’ll pull up are either postings of the doujinshi or mine. I posted these stories on Deviant Art under the pen name nullmetal and Omo org under the handle writerforce6, along with the continuation that, in ten or so minutes, will be posted in the Board Member Stories section.

Anyway, that said, I do find that I’m lost on a couple things. Sadly, as mentioned above, I have no investment in the source material, and thus am a little lacking on the context of the characters. Had I watched or read any of it, I’d at least know what everyone looked like, their general mannerisms (apart from what I picked up in your story), and what the hell any of this has to do with playing instruments. :stuck_out_tongue: Again, I feel that I don’t really have any ground to bash calling someone a bassist or guitarist, without having read anything that explains just that. But it still seems a little out of place to use such descriptions if nothing to do with the music club is actually part of this story.

Some of these questions will be answered in the continuation (such as what certain characters look like and some of how the music club fits in), so I won’t answer them here. That said, I do apologize for not describing the characters’ appearances enough, but for the record, Yui and Ui are twins… so if I described their appearance, most of the things I could say aside from clothing (which I just didn’t think of at the time I wrote this) would apply to both characters. That’s why, with the assumption that my readers on Deviant Art and Omo would have actually seen K-ON and therefore known what they looked like, I decided to refer to them in other ways.

So that’s basically a longer way of saying. "I like it, it’s good; but I don’t know what ‘K-ON’ is and don’t plan to look into it.
If there’s a way to say that without coming across as a dick, I’m hoping it involves leaving a disclaimer like this, followed by a smiley. :wink:

Compared to some reviews I’ve gotten on FFN, you sound like an angel. You want to see some genuine dickspeak? Click on this link (https://www.fanfiction.net/r/11548035/0/2/) and read the review by Agent 94, which if you’re not on mobile should be the top one. Granted, that story is like two years old, kind of terrible, was posted on an account that has since died off, and was definitely not my best work even for then, but when you read a review like that, regardless of how bad your story actually was, every other review you’ve gotten that wasn’t on that tier seems pretty kind by comparison.