Mash's (Rear) End

(Fate: Grand Order)

(Girl to ass TF)

Mash was… anxious, to say the least. The demi-servant was currently enjoying what little free time she had between all these lengthy missions, so when she woke up to find a letter from none other than BB? Something was most definitely up. The girl spent a few good minutes weighing her options before finally caving in and deciding to give it a go. Yeah, the purple-haired woman was likely up to no good, but even then, what’s the worst that could happen? Pranks were an integral part of the certified Chaldea experience, so Mash was more than used to them at this point, seeing as she was the first one of Gudako’s many servants, not to mention, the girl was… simply curious, if she were to be completely honest with herself.

Wearing her usual comfy gray hoodie and a black skirt, she slowly made her way towards the Moon Cancer’s room, greeting a few fellow servants along the way as she did so, their frequency decreasing with every step closer to the dreaded chamber. Mash touched the doorknob, half-expecting it to shock her or something, but obviously, if BB had something in mind, it would be nothing as uninspired as that. With a heavy gulp, she pushed the door open.

“Oh, senpai, you’re here! And it just so happened that you found me in such a compromising… pose…” BB was lying atop her bed, wearing nothing but a set of black, lacy, and most of all, very revealing underwear. Her blush disappeared as quickly as her eyes met with Mash’s… was she expecting someone else to enter? Without skipping a beat, the Moon Cancer spoke flatly to her visitor. “Oh, it’s just you, demi-girl… I didn’t expect you to actually come here.”

As BB’s flirty masquerade vanished, quite the opposite happened to Mash’s very own. The usually rather composed girl was beet red from embarrassment, so much so she was sure there’d be smoke coming out of her ears if she were in some sort of anime… What was the meaning of this? Sure, BB was weird-- actually, scratch that, she was completely nonsensical, but to see her like this… Why?

The purple-haired girl stood up without any signs of shame or distress and put on a red, fluffy bathrobe before turning towards her awe-struck ally. “Sorry, but this kinda sight is only available for Senpai! Still, I’m rather surprised, I assumed you’d just ignore poor ol’ me! And you actually came before Senpai, that’s even better!”

Senpai? Does she mean Gudako? But why would she… Oh right, this is BB we’re talking about… Mash took a second to gather her thoughts before responding. “So I wasn’t just imagining things, you really were stalking me and Master for the past couple of weeks!”

“Stalking… that’s a big word… personally, I’d say it was more of a reconnaissance. I thought I was soooo sneaky, but it seems like my love for Senpai simply cannot be contained, so you noticed!” BB giggled.

“Love… wait, was this… display… from before meant for Master? Surely, you don’t think she’d be interested in someone like you!”

“Even if she isn’t right now, I have my ways to persuade others… But you’re not completely wrong, as long as there’s a certain obstacle in my way, me and Senpai will never end up together.” The moon cancer threw out an accusatory glance towards her fellow servant.

“Wait, you can’t be… I’m not interested in Senpai… like that…” Mash responded unsurely. As much as she would’ve wanted to be certain… Well, she and Gudako did have a certain kind of relationship, platonic or otherwise.

“It makes no difference to me, what’s important is that she’s interested in you! But to cut this exposition dump short, let’s just say…” BB’s eyes sharpened.

“...I plan on removing that obstacle.”

As if on cue, the room’s door closed itself, locking the duo inside. Was… was this girl mad? Was she really thinking about disposing of the Shielder? But that wasn’t possible, you can’t kill like that! Chaldea’s laws make sure of it! Mash knew this, but even so, she was fearful. If there was someone out there who was able to find a way around these rules, it was without a doubt, BB. But without her shield, how could she fight? She couldn’t run away, she couldn’t–

“What’s with that face? I’m not gonna kill you! That wouldn’t be nearly as fun! But I did learn a trick or two about how servants operate while in Chaldea…” The purple-haired girl giggled as she… moved around? Mash was expecting a fight to break out, but that woman just turned around and started shaking her butt! Not only that, she took her panties off!

“What are you planning?” The demi-servant tried to ask, but this whole situation… to say it made her blush would be an understatement. In response, BB simply smirked as Mash felt herself… getting pulled closer?! She couldn’t believe it at first, but it was true! Slowly but sure, her entire body was inching closer and closer towards BB’s bare ass!

“W-what’s happening?! BB, we’re supposed to be allies, stop it at oooonce!” Mash tried to catch something, anything to work as an anchor of some kind, but anything that could serve that purpose was just so far away that the girl couldn’t grasp it no matter how much she tried. It was almost as if BB made sure to move her furniture away in case something like that happened… and knowing how cunning the Moon Cancer was, it was most likely a correct hypothesis.

And so, without any way to keep herself steady, Mash could do nothing but watch in fear as she was about to collide with her apparent love rival’s backside, only one thought permeating through her head - why?! Why did BB want this to happen?! What good would the two of them colliding do, at best it might humiliate the demi-servant a bit but at worst… the two of them could get seriously hurt!

But despite the obvious danger, BB just grinned without breaking eye contact even once… at least until the collision finally occurred. Mash closed her eyes, readying herself for the impact but… nothing. No sound, no pain… the pink-haired girl would’ve been relieved at that fact, were it not for the fact that something else disappeared.

As unimaginable and nonsensical as it sounded… The Shielder’s feet were gone.

Mash opened her eyes, sure it was just some sort of trick or servant skill used by BB to fool her but… it was true.

…No, no it wasn’t.

In fact, the truth was much, much worse. Mash’s appendages didn’t simply turn into nothingness, they were absorbed by the only other person in the room - the Moon Cancer herself.

It couldn’t be true, it shouldn’t be true but… she trusted her eyes and cutaneous senses enough to be sure as if it wasn’t evident but the way BB’s ass was violently rippling around the point where the two girls were conjoined.

And to make matters worse, the demi-servant’s situation wasn’t getting any better. Slowly but surely, more and more of her was being absorbed - first were obviously the feet, but by the time Mash made that realization, her ankles were mostly gone too…

“BB, I’m sorry! Sorry for wherever you think I did to you! Me and Senpai… we aren’t like that, you have to trust me, please! Stop this spell, I beg you!” Mash pleaded with tears in her eyes, her opponent only giggling in response, said laugh reminding her of all the psychotic yanderes she’s read about in her favorite manga. She always knew BB to be a prankster but this? This was no prank, the woman was dead serious about getting rid of her!

“Oh, Mash, you’re so funny… Honestly, I’m kinda sad that in a few minutes I won’t be able to hear you squirm anymore~ But no worries, I’m positive Senpai will just adore your new form… yes, I know she will~”

“M-my new… form?! BB, this isn't funny! You can’t seriously think you’ll get away with any of this!” Mash tried to put on a brave face, hoping it’d dissuade the madwoman from continuing but the Moon Cancer just kept laughing as more and more of the pink-haired girl was being devoured.

At this point, both of the woman’s legs were no more, instead, her torso was the part that combined the two girls together… and unfortunately, the fusion was only hastening its advance. If this kept up, she was gonna disappear in a matter of minutes, if not less!

Although… ‘disappear’ might not have been the right word… as much as Mash hated that, she knew she wasn’t gonna vanish without a trace. Even now, she still felt her legs, no matter how weird said sensation was. They definitely still existed, just not as legs anymore… and considering everything that was happening, there was seemingly only one explanation.

She was becoming BB’s ass fat.

It sounded utterly ridiculous but… her senses didn’t lie, neither did her eyes… and considering the likes of Circe, servant transformation was definitely not out of the realm of possibility.

“You… you’re turning me into your butt?!” The Shielder cried out, hoping that the seemingly only logical answer was untrue, that her apparent love rival wasn’t cruel enough to submit her own ally to this fate, but alas.

BB giggled in response.

“Ding ding ding, we have a winner! You got that one hundred percent correct! Anything you want as a reward for being such a smart tush~?” The Moon Cancer didn’t even bother hiding her excitement, and Mash hated that. How could a single woman be so inhumane?! Well… technically, she wasn’t a human, fair, but they served under the same master! They went on different missions together, fought side by side to restore singularities… why?! Did BB truly hate her that much? No, it was probably the opposite. The purple-haired servant’s love for Senpai was so strong, she was blinded by it. Reasoning with her seemed impossible, but what other choice did she have? What other…

Bingo!

God, I’m such a… why haven’t I thought of it sooner?!

“Lord Camelot!”

The lavender-haired girl yelled the name of her Noble Phantasm loud and clear, wishing its defensive properties would save her, or at the very least, slow the absorption down, that maybe her increased defense would be enough to get out of this trap, she was wishing for… anything, really. The Shielder even got her hopes up as BB seemed to lose her cool for a bit, breaking her act for a second or two, yet… nothing happened. Why?! Why wasn’t it working?!

“Phew, you got me worried for a sec there…” BB sighed before returning to her bold, confident persona once again. “That pesky Phantasm of yours was the only enigma that could’ve potentially ruined my plan, but it seems like you were too late… Good thing you decided to talk it out instead of using it right off the bat… seem like your pace-loving nature will be your own undoing~”

“My… nature? So I could’ve escaped?!” Mash broke down a bit as the realization struck. If only she was a bit more assertive, all of this wouldn’t have happened! Yet instead, she was now entering the final phases of the transformation, leaving her as nothing more than a bust hanging from her attacker’s backside.

“Yep! The only reason you were unable to use it is… well… as I’m sure you’ve realized this by now… you’re simply more buttocks than a girl now~”

As much as it hurt, the pink-haired servant had to agree on that point, and by the look of things… she wasn’t going to have any more ‘girl’ left in a few seconds…

“Speaking of which… You know, I was kinda locked in place cause of the whole ‘Demi-servant-stuck-to-my-butt’ thing, but now that you’re just a head…” BB straightened her legs as Mash’s point of view rose up by around half a meter… and then began to shake around without any rhyme or reason.

“Hehe, yup! Light as a feather! How’s the view down there?” The Moon Cancer teased as she wiggled her butt around. The girl in question would have responded, but all the jiggling combined with the feeling of her ears and scalp merging with BB’s ass made it hard to concentrate, let alone vocalize any thoughts. In a last-ditch effort to escape, however, she was able to focus hard enough to formulate a single sentence.

“Please, stop…”

And as the transformation hit its crescendo, so did the purple-haired devil slap her butt, sending waves of both pain and pleasure to Mash’s brain as a pair of black glasses fell onto the floor and the room fell silent.

“Hmmm? You were saying something…?” BB looked back at her bare ass before cackling. “That’s right, you can’t respond! You’re just my ass now! After so many months, the biggest obstacle is finally gone! Oh, and don’t think I’ll be turning you back anytime soon, if at all… You make my butt so much bigger and plumper… seriously, Senpai’s gonna love it!”

Don’t you dare call her Senpai! If you think she’ll just get together with you, you have another thing coming! Mash shouted inside of her own head, hoping it’d somehow reach her new captor, but the only thing she produced was a very tiny toot that went unnoticed by the Moon Cancer. The former girl wanted to cry, but clung on to a single strand of hope left - her master.

Surely, Senpai was better than that! Sure, she might’ve had a collection of some questionable magazines and had a somewhat dirty mind when it came down to it, but Gudako wouldn’t fall into such an obvious trap, even if BB’s ass was a sight to behold.

Huh?!

Why… Why did I just think of that?! Mash cringed a tad as she replayed that last sentence a few times in her mind, but decided to ignore it for now. It was just a slip of a tongue. Yeah. Totally…

Yet despite all that, a small part of her felt weirdly proud of BB’s compliment towards her size. If she was an ass, the least she could hope for was being a nice and juicy one, right?

…Right?

***

Gudako was… intrigued, to say the least. She knew BB was sort of a… special case, to put it politely, but the young master never would’ve expected the girl to be so forward as to send her a straight-up love letter… This was certainly quite a shock to her system, seeing it first thing in the morning but… she couldn’t ignore it. While the offer didn’t sound unappealing, Gudako knew she had to nip it in the bud, otherwise, who knew what the Moon Cancer was going to do…

And so, the redhead entered the lion’s den.

“Oh, senpai, you’re here! And it just so happened that you found me in such a compromising pose…” BB was lying atop her bed, wearing nothing but a set of black, lacy, and most of all, very revealing underwear… the lower half of which seemed to be barely able to contain the servant’s juicy ass.

Gudako blushed slightly, but was able to get back to her senses rather quickly. “BB? I got the letter. I understand how you feel but…”

“But? The only butt you should care about is this one~” The Moon Cancer slapped her behind lustfully, once again sending waves of conflicting feelings through Mash's mind, as the Shielder tried to yell at Gudako to run away… but how could she? It’s only been a few minutes since her transformation, but the former girl had apt time to learn how powerless she was… So much screaming and crying happened in such a short amount of time… if she were still human, she certainly would’ve lost her voice by now… but of course, she wasn’t.

She was just a butt now, one that was in a constant state of pain as BB’s lacy underwear dug deep into her new, plump body… and she hated how she was slowly getting used to it all…

“No, BB… me and Mash… look, I appreciate the effort, and I do think you look good, but I just can’t!” Gudako rebuffed any and all advances, but the purple-haired servant saw right through her. This deep blush that adorned her cute face said it all, not to mention how she trembled from excitement… All she needed to do was push the right buttons, and Senpai would be hers!

“Mash? Wouldn’t you know it, we just talked a few minutes ago, about her love life, no less…”

“You… you did?”

“Yep! Suffice to say… your affection is one-sided…”

What?! You liar! You– The Shielder was furious. How could she just say such untrue things when she was right there…?!

…Oh, right… Of course, she could, after all… asses can’t deny, or just talk in general for that matter… Still, there had to be something she could do, right? While Mash was more than sure of this new form’s limits, at the very least, she decided to try to communicate by any means possible. The pink-haired servant produced a noise so loud and horrid it almost put Eli-chan to shame, yet even then, she was unable to break through, as no voice left her mouth… but the protest did do something else…

PPPPPPPHHHHRRRRRRBBBBTTTTTT!!!

The smell and taste of a horrid fart filled Mash’s mouth as it erupted into a violent cloud of green gas.

Did I do that?! Bleh, I can feel everything! My mouth, my tongue, my nose, all of it…

Yet as unpleasant as the experience was, the girl-turned-butt couldn’t argue with the results… Surely, she was able to make a complete fool out of BB! Now Gudako was-

Mash did not finish the sentence, as her mind was overwhelmed with yet another feeling, this one completely unrelated to her tasting or smelling capabilities… the sensation of pure, adulterated pain, as BB took barely any time to punish her former ally.

Gudako could only look in shock at this sequence of events. First, the Moon Cancer ripped a rather fat one, and now she kept jumping up and down, as if the girl wanted to punish her backside for misbehaving. It was certainly an unusual sight to behold, but somehow… Gudako couldn’t help but giggle? It was disgusting, rather crude and a lot of other things but… even if she was forced to pinch her nose in self-defense, it was (ironically) rather refreshing to see BB genuinely flabbergasted, even if it was for a single second.

“U-um… Sorry about that, I ate some… stuff I probably shouldn’t have… but I promise that’s not gonna happen again!” The trickster put heavy emphasis on that last part, making sure Mash heard her… otherwise, the punishment was only going to get worse.

Alas, Mash wasn’t listening. Not because she was continuing her rebellious streak, but simply because… she couldn’t. Her mind was absolutely overwhelmed by the repeated smashes her new, tushy form was forced to endure against BB’s bed. All the pain and… weirdly enough, pleasure simply made the demi-servant short circuit for a bit before she was able to regain her senses, but by the time she did…

Her Senpai and BB were already hitting it off. The girl’s nonexistent eyes were met with Gudako’s still-very-much-existent peepers and… wait, did that mean Senpai was staring at that woman’s butt?!

“You know, seeing you so… vulnerable was pretty neat… you should do that more often I think!” The redhead blushed as she looked over the servant’s plump butt. She still had her doubts about all of this, and she wasn’t even sure if trusting BB’s words was really a smart idea (it wasn’t), but… she almost felt compelled to, in a way. She couldn’t put her finger on it, but ever since she entered this room… the Moon Cancer kinda reminded her of Mash, in all the right ways… Especially that plump bottom she saw every time the Shielder jumped in front to protect her…

It was a completely irrational way of thinking about it, and Gudako knew that all too well but…

Love is rarely rational, isn’t it?

Instead of fighting her base instincts, the master decided to just give in and enjoy herself while she could. Whether BB lied or not, it’s not like it mattered, right? Mash didn’t have to know about this! And so… with the deepest blush she ever had, the redhead asked.

“Can you… sit on my face?”

BB grinned.

“Gladly~”

Without a moment to waste, Gudako locked the door tight, jumping onto the bed immediately after she checked if they were truly locked. Her purple-haired date caressed her senpai’s still red cheeks, producing a giggle out of the master. Shortly thereafter, Gudako’s face was bathed in shadow, BB’s massive rump taking up most of the girl’s view as Mash was once again forced to stare at the woman’s admittedly pretty face… but it all seemed so wrong! No girl should ever be this close to another’s butt unless they were dating, or better yet, married! Or characters in a lewd manga, then it made sense! Not… there! That’s not how she wanted to get her first kiss!

Mash would’ve once again tried to communicate and stop the two, but… as much as she wanted to embarrass the woman that forced her into this tushy form, farting at Gudako’s face point-blank just didn’t seem worth it…

Actually, a now alarmingly large part of her didn’t feel any act of rebelling was worth it, not even thinking about it. Being a human was fun in its own way, but becoming a butt was so much simpler… no human responsibilities, just jiggling and–

No! I have to fight! I’m Mash Kyrielight, not some bimbo’s rear end, I’m–

“Say aaah~~!”

*thwomp!*

At once, the shadow turned to complete darkness, the two girls’ cheeks meeting at last as Gudako welcomed the warm embrace of BB’s massive ass.

N-n-no! This is so weird! Is… is Senpai licking me?! How degenerate can this girl get?! Yet as the agonizingly long seconds of silence went on it started feeling… correct. That’s what she was supposed to do, right? Wasn’t this her calling in life, to make Senpai happy? If anything, this new form was way better! Now she could focus on it properly since it’s not like she really had anything better to do… But fate was a cruel mistress, and just when Mash finally started enjoying this new existence, BB raised her butt…

What? No… no, no, no! Back, I want back! Let me kiss Senpai, please! I need her!

“So, how was it, Senpai~?” The Moon Cancer looked down, but her master’s happy, sweaty face told her all she needed to know.

“Simply… divine… I asked Mash to sit on my face once, but she just looked at me weird… your ass is sooo much bigger anyways though, I don’t mind that much now…”

I… I did that? Why?! Why was I so dumb, why did I refuse?! Stupid Mash, stupid! You made Senpai sad, how could you?! The butt sobbed.

“Well… she can’t refuse now! Go ahead and taste her as much as you want~” BB teased, giving her own butt a knowing look.

“Can’t… refuse? I don’t think I follow, but I don’t care… Just sit on me some more…”

“You don’t need to tell me twice…” The girl lowered her butt once again, the second time of many… and the day just started! Oh, what fun the two of them were going to have… with no annoying Shielders in the way BB finally had Senpai all to herself! She simply couldn’t wait to have more ass fun tomorrow, and the day after, and the day after that, and… hopefully, the pleasure was never going to end!

And whether BB realized it or not, Mash certainly didn’t mind that arrangement either~