[ABDL, Diaper Use, Soiling, Weight Gain]

For the Knight of Betrayal, there was a laundry list of things she hated. Most of all the circumstances of her birth, her parents, her allies, and so on and so forth. But all of that honestly paled when compared to her current situation.

Just a scant month ago, she was stuck in a Singularity together with the Japanese Berserker, Minamoto no Raikou. Or Mama, as she now called her. And while they were there, Mama was the only one who could take care of her.

Unfortunately, they were both affected by the singularity. And the two humans were twisted into forms that were still humanoid, though nowhere near graceful compared to their usual selves. They were forced to take upon the visages of the Oni that had conquered the pocket of history, with both of them devolving into pure filth. Whether it was the older woman, or the younger Knight.

But that was then. And she thought it was over after they got back to Chaldea. Unfortunately, it was far from over. Because while the Berserker was able to regain control of her body, the Knight was not so lucky. She was stuck with a permanently sensitive set of bowels, one that could easily ruin her composure should she miss as much as a single step. This was her curse. This was what she was forced to handle.

It was why she tried to avoid Mama as much as possible. But eventually, she couldn’t. Because Mama had rubbed off on her too much. And the second she ended up in her arms, she started acting like the little oni she had been turned into, suckling on her Mama’s breasts and filling her diaper without a care in the world.

After having gone through this routine far too many times, their Master decided that it was best for the two to stay together as long as possible. To make sure that Mordred could end up recovering and becoming an adorable Saber ready to slaughter her enemies once more… And make sure she would stay potty trained.

The other reason their Master decided to approve of this situation? Simple. Raikou was fighting with even more vigor than usual. In fact, whenever she held her blade in one hand and her dearest Mordred clung to her body? She was able to swing it with such power that she could outright shatter singularities if she wasn’t careful. That increase in power was a great reason to keep them together.

It was just something that Mordred had to deal with. And deal with it she did, regardless of the consequences…

---

“Mordred? You need to eat, you’re not going to grow big and strong if you don’t.”

The Knight of Betrayal huffed and puffed and turned her head as the spoon moved towards her lips. She wasn’t hungry. She had lun-lun just a few hours ago, she was still full! And even if she wasn’t full, she didn’t want dinner!

Why? Simple. She had gotten way too complacent. She could barely fit into her jumper, and the straps were struggling to hold up her weight. It was utterly and horribly humiliating! She didn’t want to be this big, and she especially didn’t want Mama to bring attention to it!

And yet, there was no way that she could escape the reality of her situation. She was fat. Unbearably fat. Like, if you compared her width to that of her Mama’s breasts, which were heavy in their own right? She was like, twice as fat as they were wide. And that wasn’t a good thing! She was supposed to be a proud knight, not some fat baby who could barely waddle without toppling over.

“Oh, Mordred. You really, really do need to eat. You know you get this way when you’re hungry. Come on, just open up and let the airplane land on your tongue.” Mama said, her worried expression ever-present.

She knew it was her fault that the little girl had gotten so big. But at the same time, it was what made her so happy. The little girl depended on her. She needed her. And it was thanks to this need that she was able to swing her sword with all the power that supported her. Without the little fat baby by her side… She wouldn’t be nearly as strong.

Mordred kept huffing and puffing, refusing to let a single bite in. Even as her tummy started to throw a fit. She was going to rebel against her new size! She was going to rebel against Mama for making her this big! And most importantly, she was going to rebel against-

Her cheeks flushed bright red as she felt her bowels contracting. Of course, the second she thought about her poopy problems, she just had to have an accident. And a big one too, because she could feel the thick sludge trying to squeeze its way out of her tight hole. She struggled and strained, her cheeks flushing bright red in the process…

Slowly but surely the bottom of her diaper, kept trapped within her cute oni-themed onesie for only a brief moment before the buttons popped off, expanded as the terrible stench of her mess started to waft around her. The loud crinkles filled the air, making her embarrass herself further and further as she acted like one giant baby. Just filling her nappy whenever she had to…

Mama smiled slightly as she got up, putting away the mushy food on the nearby table. “Just sit still, Mordred. Mama’ll get you a new diaper. Okay?” The tall mama chimed, happy to see her little baby girl slowly fill her diaper. It meant that she’d be less cranky when it was time to nap.

Once Mama had left the room, the baby in red’s messy accident came to a quiet end. And the heft of her poopy started to weigh her down more, to the point where the straps on her jumper were struggling-

*SNAP*

Scratch that, they had given way. It took but a second more for Mordred to fall straight down on her thoroughly pooped seat, her heavy body causing it to squish all around inside that diaper and thoroughly mess it up in the process. She was utterly and completely soiled, and yet…

Despite the tears building in her eyes from having turned into this humiliating mockery of her past self, she was now free. And if she was free, that meant that she could get away. Or… Orrr….

Her tummy was starting to rumble as she looked up at the shelves far above the table. Shelves that had several cookie jars. Part of why she had been getting fat was due to the way her Mama spoiled her with all these cookies. But now that she was free, and since she wanted to show her Mama that she could be a bit independant so she didn’t have to feed her too much…

Stealing those cookies was the way to go. Even if she felt weighed down by this enormous load in the back of her diaper. All she had to do was climb onto the table and reach up as far as possible. That was all she had to do.

It really wasn’t a difficult task. But the fact that Mordred, the Knight of Betrayal, the girl that had inflicted a fatal wound on her own Father in the far past, was now little more than a fat baby who could barely walk in a straight line on a good day? It was a lot harder than she made it sound.

Even when she summoned Clarent, the sword that stuck by her side in all fights, using it to try and vault herself onto the table? She could barely manage to lift herself. And it wasn’t just because she had gotten super heavy and had a bunch of her own poopy in the back of her diaper…

No, it was because she had lost a lot of her own strength. The reality of the situation was linked to her dependency on Mama. The more she needed Mama to help her, the more power Mama sapped from her. She knew it wasn’t intentional, because Mama wasn’t trying to hurt her, but it didn’t make it any less frustrating.

“Come on..! Come ON!” Mordred shouted as she pushed and pushed, barely lifting herself off the ground. The butt flap of her onesie waving back and forth as her sword struggled to support her weight.

She could almost grab onto the table! She could almost lift herself up if she applied herself! She was almost there! And yet despite this ‘almost’, she just couldn’t get past that little barrier. She didn’t have the strength. She didn’t have the power. She was just a big, fat baby. A mockery of her old self.

And as she felt her grip slip, and Clarent crack to the point where it was forced to dematerialize, she was forced to land right back down on her rotund rump, her poor diaper taking another blow. She could feel the poopy mushing its way all around her, and she could feel the shame of failure settling in once again.

She was a complete and utter waste. She couldn’t use her sword, she couldn’t even lift herself onto a damned table. She was just a little baby that couldn’t do a thing without her Mama.

“Oh, Mordred… You poor little thing…”

And right there, on cue, was Mama in the flesh. She also brought three fresh diapers with her, to make sure that she’d stay dry despite her massive messes, and a new bottle full of nutritious baby food. Because the poor girl had gotten so weak to the point where she could barely even chew food…

Mordred looked up at Mama and the tears started rolling. She didn’t like this. She didn’t want this. She just wanted to go back to her life as a Knight. Even if she was destined to die on the battlefield thanks to everything that had gone on behind the scenes, it’d be less humiliating compared to this life.

That’s what she thought. But as she opened her mouth to start wailing…

Mama finally managed to slip a spoonful of food into her mouth. And the hungry baby slowly swallowed it, the tears still rolling down her face. She could feel the grumbly in her tummy slowly die down as she swallowed the nice baby food, her hunger satiated…

“There. Wasn’t that better, Mordred?” Mama said, smiling from ear to ear as she kneeled down to look her little baby in the eye. “No more tears, no more bratty tantrums. Just eat, okay?” She said, smiling as brightly and as convincingly as she could.

Mordred slowly nodded with the spoon in her mouth, opening her mouth again to allow a bit more in. And then the rest in the span of a minute or so, the rapid feeding keeping her placated. The shame was washing away…

In fact, the shame was pouring out through her thighs, her cheeks blushing brightly as she slowly tried to get back up. She didn’t like the feeling of pee and poopy mixing together. Even when she was being fed.

She didn’t manage to get up, because Mama was there to stop her. “There there, Mordred. Let Mama give you a change, then you can go sleep. And everything’ll be okay when you wake up. Okay?”

The baby wanted to rebel. But at this point, her satisfied tummy made it hard to do so. She just laid right there, and let the diaper slide off her waist after being undone.

Changing her took barely any time. And despite the fact that there were three diapers, the way the poor girl’s legs were being spread apart hardly imparted more shame upon her than it already had…

Mama Raikou lifted the little girl back into her arms, carrying her with all the power she had unintentionally sapped from the baby, as she slowly rocked her back and forth. Humming a tune from her childhood, a lullaby that would make her drift off to sleep.

Mordred yawned and slowly let her eyes flutter. Mama’s lullaby was really effective, and… W-Well… Even if she felt a lot of shame from how heavy she was, and how she wanted to show she was independent… There was always another day.

And with that thought in her mind, the oversized and humiliated baby fell asleep, snoring peacefully in her Mama’s arms...