[ABDL, Soiling]

"Oh, little Illya. I'm very happy you decided to invite me over. I thought you were starting to grow out of your Little cravings, but it looks like my sweet little baby girl is still the same as always."

"That's right, Mama Luvia. But I wanted to show you something before we get started, okay? It's part of why I called you over, and once it's over and done with, we can have lots and lots of fun like usual."

"Ohohoho. Of course, my sweet little baby girl."

An unusual yet common sight was making its way through the Einzbern manor. A blonde girl and a much smaller girl were walking side by side. Luviagelita Edelfelt and Illyasviel von Einzbern. They weren't public known as good friends, but after the latter had hired the former through a site that guaranteed a loving and maternal relationship, they had started to form a strong bond. Like that of a Mother and her infantile little child.

The thing that made their presence together even more unusual was two traits that stood out about Illya. The fact that a couple of buttons had popped on her normal dress, leaving her plush and plump little belly sticking out. But the garment that it partly rested atop of was perhaps even more concerning, the large and crinkly diaper that she wore whenever Luvia came over to spoil her. It was something that she had to wear as a part of their agreement, and something that she had come to love quite a lot since it brought her a sense of safety.

Luvia had originally been quite surprised to find that she had been hired as a Mommy by one of the former Masters of the Fuyuki Holy Grail War, but it didn't matter too much. Partly because she actually shelled out every little bit of cash that she asked for as part of their agreement... And partly because she had grown quite attached to Illya at this point. Who wouldn't, when she turned out to be one of the cutest babies? So playful, yet so wellbehaved that there was nothing that she needed to worry about. Which was probably why she spoiled her so much and ended up making her grow a bit too heavy. At least it didn't matter, little Illya had practically retired from the public, which meant that she could indulge herself and hire Luvia more often. A thought that filled the maternal Magus with a lot of warmth...

"Okay, we're here!" Illya chimed as she opened up the door to one of the nurseries that had been specifically built to allow the young girl to indulge in her infantile habits and loves. Smiling as her blonde Mommy walked in before her, a sly smile growing on the white-haired little Baby's lips.

Luvia suddenly froze in place a few seconds after she had entered the nursery. Not only was this a second nursery within the manor, which was enough of a red flag to make her consider what exactly her little baby did on days when she hadn't been hired... But the brunette that was currently laying down on the floor, idly drawing with her red crayons was far too familiar. There was no way, right?

"T-Tohsaka?"

The brunette froze as she heard an equally familiar voice, causing the twin-tailed girl to turn around. It was one thing to be hired by Illya to be her adorable baby girl, suckling on a paci while adorned with the biggest nappies and the cutest onesie that really brought out every little bit of babyhood in the older Magus... And it was another to suddenly be confronted with her rival, who looked like she was ready to take care of somebody like her.

"L-Luvia?!" Tohsaka Rin, the Rental Baby that had been occupying this separate nursery, felt her face turn so red that she probably looked like a tomato. All while she tried to crawl away from the blonde to try and stop her from looking at her in this humiliating state. Why was she here!? What had Illya done!?

As much as she could find some sort of twisted delight in seeing her rival like this, Luvia had a few principles as part of her role as a Rental Mommy. There were very strict rules regarding extra babies and humiliating those that fit the label of a 'Baby'. But more importantly, she had been hired to baby Illya. Tohsaka was not a part of that deal!

"Illya, sweetie..." Luvia twitched a bit as she used her maternal voice in Tohsaka's presence. She'd probably tease her over the fact she could pull off a role like this with no issue. "Y-You have quite an adorable baby sister. But Mommy-"

Before she finished, the door to the nursery not only slammed shut, but both girls could hear the audible sound of the lock being turned. They were locked inside the same room regardless if they wanted it or not.

"Sorry, Mommy! Sorry, little Rin! I've lost the key, so you two better get along!" Illya chimed from behind that thick sheet of wood. When in reality there was no such thing as losing a key when all of the locks were sealed with magic. The reality was that she had trapped them together in one of their mutually most humiliating states. What for? Neither of them could really tell from the onset, just that they didn't want to be here.

Luvia slowly sighed. Very well. She had a duty as a Mommy. If she wanted to earn her paycheck, and if she wanted to keep up this tender relationship that she had come to appreciate, then she had no other course of action.

Rin slowly peeked out from an obnoxiously large plushie, one of several that dotted the nursery. She didn't like this at all. It was one thing for her to suddenly develop a bout of stress from how intense studying had been, it was another for Illya to offer her help in the form of capital and spending some relaxing time with her as a Baby. To then rope in one of the causes of said stress, right on a day when she wanted nothing more than to just indulge and be a good Baby who didn't need to worry about anything..?

The brown-haired Baby trembled as she tightened her mitten-covered fist. She really didn't want this. And to make matters worse, her dislike for this situation was quickly causing her stress to spike. If this kept going, she wouldn't be able to... able to...

Both of the two Magi heard the sound of something foul slipping out of Rin's hindquarters, with the brunette quickly blushing and trying to hide behind the enormous plushie once more before the worst part of her current state kicked into effect. Even as she heard Luvia getting closer and closer with every passing moment.

"D-Don't come near..." Rin muttered, her voice muffled partly by the pacifier in her mouth. Her bowels were straining and cramping more and more as her heart slammed against her chest. She just wanted to relax, she didn't want to go through something like this. Damnit, Illya..!

Just as Luvia poked her head around the enormous teddy bear that served as Rin's sole source of safety, she noticed the big Baby squatting down onto her knees, a few tears quietly rolling down her cheeks. All while she seemed to strain and hold everything in. But she couldn't hold it in. Her efforts to try and resist folded very quickly as another brassy sound left her buttocks...

And the poor brunette was forced to accept defeat as the back of her diaper started to expand. Not just a little either. It was expanding rather violently. So much so that it popped open the buttons on her onesie, and any little trace of white on the back of that padded garment very quickly turned a deep and disgusting brown. It wasn't just that Rin had managed to shit herself, it was that she had shit herself so hard that she couldn't even try to hide it.

In any other situation, especially if she had caught her soiling her panties, Luvia would've mocked her rival. But seeing her like this, dressed like the same kind of baby that her dear little Illya was, her heart started to tremble ever so slightly. Should she really mock a Baby for something they couldn't control? Was she that cruel? Perhaps, but in this very moment, she chose to do something that would no doubt strike Tohsaka as out of character.

"There there." Luvia muttered as she kneeled down to be at eye-level with the rented Baby, slowly running her hand through the Baby's hair. All to try and add a little bit of security to the girl that wanted all of this to stop. "It's all going to be okay. Mommy is here for you, little Rin." She said in a soothing and motherly tone. Even if it would give the girl whiplash. Because she wanted her to feel safe when she was near.

Rin wanted to back away from the blonde Mommy. They were rivals, she wasn't supposed to help her... h-help her? Wait, what was she doing? She wasn't mocking her? T-That was a first. Normally, Luvia would take any chance she had to mock and fight against her over incredibly trivial things. But here she was. not trying to compete, just trying to help her and make her feel like she shouldn't worry...

It was... A bit more effective than she would like to admit. Something about Luvia made her really fit this kind of role. So much so that the tears began to slow down and eventually dry up, all while the little Baby started to snuggle her and hug up against her to try and get a bit of that wonderful warmth and comfort.

Luvia smiled as she felt little Rin's arms wrap around her. This was a first for her. Normally they were more likely to fight against one another until one of them passed out. To hug it out like this was... Well, there was no better way to describe it than satisfying. She would hate to admit it, but part of why she had served as such an adversary to little Rin was to both toughen her up so she could handle the harsh Magus world, but also so the two could bond. A hug like this was a sort of reward, to tell her that she had...

Before she could let that train of thought depart the station inside her head, it came crashing to a halt thanks to the bubbly sound of her little Baby making a bigger mess inside her diaper. An act that made the brown-haired Baby blush even more than she already was, desperately trying to hide her face and hide away from the world at large.

"Little Rin... Did you make a big oopsie..?" Luvia did her very best to maintain that maternal tone. It wasn't actually hard, now that Rin had shown her such a cute side of her. A side that actually responded affectionately toward her. But just so her Baby couldn't try and lie, she reached down a bit...

Rin slowly but surely nodded as she didn't want to try and hide things. Mommy Illya had taught her that hiding accidents was a bad thing, because then she could end up making the manor all sorts of stinky. So she just had to be honest about making messes, otherwise...

Her eyes widened as she suddenly felt her Mommy's hand pressing against her diaper. N-No, that wasn't good, she was very sensitive to that sort of thing. Mommy Illya had taught her to masturbate by pressing her own messies against her butt and then really mushing it all around to push her closer and closer to a climax. If Mommy checked her now, then..!

Just as Luvia confirmed that yes, little Rin had managed to make an even bigger oopsie than before, she was quick to realize that the poor Baby's face had turned red once more. But not out of embarrassment. No, it was clear that she had just experienced a rush of something more adult, given the trail of drool running down little Rin's chin.

"Oh, little Rin... Illya's been teaching you really naughty things, hasn't she?" The rental Mommy muttered. Honestly, she should've seen this coming. She had to teach the girl to stop being so lewd during their sessions. A couple of spankings for trying to make love to Mommy, and showing up wearing one of those diapers that had cut outs in them. The silly girl had a libido that couldn't be tamed, and she had inflicted some of her needs onto her Baby in turn...

Rin blushed brightly. Mommy Illya had done a lot. And all of it had soaked in thanks to how thoroughly she had babied her. How was she supposed to forget what it felt like to climax from her poopies? It was hard. But at least Mommy didn't punish her for enjoying it...

Luvia took a deep breath and lifted her oversized Baby into her arms, letting her keep her arms around her Mommy to make sure that she wasn't going to fall, all while she carried her over to one of the changing tables that dotted the nursery. Which just so happened to have a storage full of milky bottles near it. Good, she could feed Rin when she was done giving her a change.

Rin blushed even more as she was laid down on the changing table, instinctively spreading her legs to make it easier for Mommy to give her a change. Not that it was particularly difficult considering she had just blown out the hatch on the back of her onesie that caused her diaper to jut out so much. She was still painfully embarrassed about making such a big mess, so much so that the Baby covered up her face with her mittens to try and avoid making eye contact with Mommy and making this an even more shameful experience.

Getting the little Baby's onesie off to the point where she could be changed wasn't very difficult. Not just because of the flap that had been blown open by the earlier mess, but also because there was a rather convenient little zipper near the crotch that had already started to give thanks to the pressure of the diaper. Unzipping it fully and allowing access to the Baby's waist from there was easy...

Luvia held her breath a little as she undid the tapes on her little Baby's diaper, and very quickly tossed that stinky mess straight into the nearest pail. Which was only part of giving little Rin the change she needed. All those stinky bits of poopy were still clinging to her plush... Hold on, had she gotten fatter?

As Mommy scrubbed away the bits of poopy that had stuck around, she couldn't help but notice the fact that the poor Baby's tummy was jutting out more than a little. Yeah, she had gotten fatter. That would explain why she hadn't seen her around as much. She was indulging far too much in all of this, and just like she had spoiled Illya and let her grow a bit too chubby, it seemed like Illya had spoiled her Baby a fair bit too. In fact, her plush tumtum was proportionally way bigger than Illya's... Which meant that if she ever took that onesie off, she'd have to come to term with the fact she had grained way too much weight for a Magus.

Rin, by comparison, was just trembling the entire time as Mommy cleaned up all the bits of her oopsie. It felt really nice, but she wasn't supposed to be enjoying it like this. Mommy Illya had been far too thorough when she cleaned her, which caused her to feel all sorts of adult shivers when she got a change like this. At least Mommy didn't touch her naughty spots, then she would've climaxed again...

Once Luvia had wiped all of that dirty stuff down and left her sweet little Baby looking completely spotless, it was time to get her in a brand new diaper. Picking out one from the supply near the table, she grabbed the one that happened to be covered in cute little pictures of the Baby's former Servant. That cute blonde with the big sword. She was adorably depicted on this padding, it was a perfect fit for somebody as naturally adorable as little Rin.

The process of slipping it on was simple enough thanks to the Baby knowing what to do. The diaper went underneath little Rin's preciously plump butt, then it went through her thighs, and finally the wings were snapped shut. Once it was secured and snug around her waist, Luvia could easily zip up the onesie and fit the flap right back on the butt, making sure that her sweet little Rin looked as cute as possible.

Rin suckled on her paci throughout it all to try and calm down and stop herself from getting a bit too aroused, but once she was back in a clean diaper and she could look up at the proud smile on Mommy Luvia's face... She couldn't stop herself from narrowing her eyes and looking away like the tsundere she was at heart. "Y-You're good at this, Luvia." She muttered, breaking character for just a moment.

"That's Mommy Luvia to you, little Rin. You make an adorable baby too, for the record." Luvia shot back as she lifted the brunette into her arms again, before grabbing a bottle of milk from the nearby storage and stuffing the rubber nipple into the young lady's mouth. As a reward for being a good Baby who didn't make a fuss about being changed or being babied by her rival-turned-Mommy.

Rin slowly closed her eyes as she started suckling from that bottle. It was nice. Maybe... Maybe this wasn't so bad after all. As long as Luvia didn't tell a soul about what they had been up to, then she'd enjoy being Mommy's little Baby...

And while all of this was happening, Illya could only giggle as she watched from afar. Her plan to make those two get along for once had been incredibly succesful. Sure, it took a lot of money to make sure that they were both there on the same day, but it was worth it.

Next time, she'd have fun with them too. Then Luvia'd have no choice but to be as perverted as her and little Rin, ehehehe...