KINKTOBER DAY 17: Ass expansion (comm from anon)
Plus Ultra provides a mating service for Alphas where they can pick their favourite Omega, have them physically adjusted to their tastes, and then fuck them. If they like them, they mate them, if not, the modifications are +

undone and the Omega is placed back into selection. The physical adjustment Quirks allow the user to produce pills that will alter physical appearance whilst providing pleasure to the individual, so there's no pain involved. Still having Omegas objectified and lined up for +

display, so all the Omegas are paid generously. The Alphas have to pay a high fee just for entry, with extra for physical changes, and then finally to mate the Omega. These profits are split 70/30 between the Omega and the company. Therefore, Omegas who join are well compensated+

for their service. Besides, because of the fees, they end up mated to rich Alphas who can look after them. Only the most elite Omegas are accepted, and every Alpha who wants to use the service has a background check run on them. So when Bakugou Katsuki's background check is run,+

the company is practically tripping over itself to open their doors to him. Katsuki strolls in with his hands thrust in his pockets, looking around. There's no shame in this method of finding a method, it's actually quite /popular/, so Katsuki doesn't disguise himself. He's the +

CEO of one of Japan's biggest international companies, and he doesn't have time for shitty romance, so he might as well find a mate that gets him hard they way he wants it. He's led to a room set out like a solo dinner date, with a beautifully decorated surrounding area. The +

idea is that he gets to meet each candidate alone for half an hour, and if he clicks with them, he doesn't ring for the next one.
It's been three hours. Katsuki scowls as a tall, slim Omega talks about how she deserves to be the mate of a billionaire.
"It's like, practically my +

birthright," she claims, not touching her food. "My parents are rich, I'm pretty, and I'm sooo good in bed, you should see."
Katsuki nods. And then he presses the bell. As she leaves in a dejected huff, Katsuki wipes his hand with his face. If this next candidate is as awful as +

all the shitty extras he's been forced to talk to, he's going to leave, mate be damned.
The Omega who sits down in front of him is without doubt the most gorgeous one he's ever seen. Green curls, a kissable pout, starstruck freckles, and bright green eyes. Katsuki leans forward.+

"Good evening, Omega," he grins, leaning his chin on his hands. The Omega raises an eyebrow, utterly impressed.
"I'm Midoriya Izuku, actually," he corrects. "Call me Omega without my consent one more time and I'm leaving. This isn't just for you. And let me say this right now: I+

am not your property, and never will be. If I give myself up, it's willingly, not because you said so. Anyway, I gather you've been here for a while: any recommendations from the menu?"
Katsuki is smitten.
"The katsudon," Katsuki responds, pointing it out. "Unless you can't +

handle a little /spice/, Deku."
"/Izuku/, not Deku," Deku says. "And I can definitely handle spice, katsudon is amazing."
"Deku's good enough for me," Katsuki says, teasing him a little. Deku rolls his eyes, biting his tongue before he responds:
"Of course it'd be good enough +

for you, /Kacchan/."
"Oi, what kinda nickname is that!?" Katsuki retorts. Deku grins then, and /fuck/, he looks sexy as hell.
"A sweet one, big boy, I'd learn to live with it," he purrs, ordering the katsudon. "So, are you one of those dickheads who likes to heavily modify his +

potential Omega?"
Katsuki shakes his head.
"Nah, and you're /perfect/ anyway," Katsuki smiles, admiring the light blush on Deku's face. "There's only one thing I ever change."
"Yeah? What's that?" Deku says, leaning in too. The two are close now, and Katsuki can't deny the +

chemistry. There's no doubt about it: he wants Deku.
"I like a big ass," Katsuki shrugs. Deku frowns.
"I'd like to say I have a big enough butt," the Omega responds.
"Not a chance," Katsuki snorts. "You underestimate how much I'm into it."
"Of course you'd be a perv," Deku +

mutters, but there's no bite behind the words. They stray to other topics after that, and Katsuki finds that Deku's personality is as perfect as the rest of him. They have similar interests, and Deku's smart as fuck. Every second they spend together just convinces Katsuki more: +

Deku's the one for him. And when an hour an half passes without him ringing, the manager knocks, letting them know that they need to make a decision: do they progress with their relationship or not?
They blurt "yes" at the same time, and the manager laughs.
"Well, in that case +

I'll have an assistant help with paperwork and set you up for the next phase!"
"You really wanted to continue this that badly, huh, Deku?" Katsuki smirks as they head towards the assistant's office.
"Oh please, you said the same thing!" Izuku defends, smiling too. Fuck. It's +

weird how much he likes the nerd already.
"Alright," the assistant says, once they've both sat down. "So you'll be meeting each other daily for three months, and then the mating session will happen. On the day of the mating session, Midoriya will first take the physical +

adjustment pill, whilst Bakugou watches from a separate room, and then once the transformation is complete, he will be free to enter for sexual intercourse. After this, you may mate each other. If at any point either of you wishes to end this relationship, you have every right +

to do so, and will be compensated accordingly. But for the sake of organisation, all payments will be made now. Midoriya, sir, please look over the document enclosing the physical changes and the fee paid to you."
Deku gingerly takes the sheet, reading over it.
His jaw drops. +

"Absolutely not!" he exclaims, turning to Katsuki. "This is at least four times my current size, and my ass isn't even small as it is! Do you know how inconvenient it would be to /move/ with that kind of-"
"Deku, just look at the fee," Katsuki sighs. He likes it /really big/, so+

the fuck what? He's always been like this. He's impressive, his job's impressive, why shouldn't his mate look impressive? He only settles for the /best/, and the bigger, the better.
Deku does as Katsuki asks, eyes widening at the number. His shoulders sag after a moment, and he +

breathes in deeply.
"Fine," he grits out, signing the page. The assistant smiles at him.
"If it's any comfort, the bigger the adjustment, the more pleasure it brings you," she reassures, tucking the page into a file. "Well, anyway, we'll begin with the daily dates. Here's the +

day we've set for the mating, it should work for you both!"
Deku and Katsuki both look over the date.
"That works," Katsuki says, as Deku hums. They can't help but to glance at each other. This may be the start of a lifelong relationship, it's a big deal. But they're ready.
***
+

(I have missed writing stuff I enjoy, and I'm really looking forward to this, so excuse me if I'm excessive but I sure as fuck did NOT miss the tweet limit, stupid bitch)

Izuku bites his lip as he walks into the fully equipped bedroom. The bed is luxurious, and Izuku flops back on it as he holds the pill up to the light. Today is the day. He's been with Kacchan for a fair amount of time now, and there's no doubt in his mind about wanting him all +

to himself. He'd been skeptical of the billionaire at first, but Kacchan really is amazing. Not just for his success, but for the way he acts, his kindness and humour and aggressive caring nature. Izuku's not worried about being mated by Kacchan. In fact, he's looking forward to+

it. Kacchan is stunning, and Izuku's been masturbating with four fingers in his hole every night since they started courting. He can't wait for that knot to finally take him. No, it's the pill that makes him bite his lip. He'd seen the measurements on the page. Kacchan really +

does like big ass. In fact, he'd go as far to say that 'big ass' is an understatement. /Huge/ is more fitting, but if Izuku overthinks it any more than he already has, he's going to back out, and he doesn't want that in the slightest. So he sits up, turning around to position +

himself so that his ass is facing the wide one-way mirror where Kacchan will be observing from. He sits with his legs spread, ass propped up against his feet as he arches his back a little to better display his ass from where he knows Kacchan is watching. He swallows the pill. +

At first, nothing happens. Obviously, he doesn't expect it to, but the waiting is a little weird. And then he feels a tight heat in his lower body, his hole wettening with slick from the arousal. He moans softly, grinding slightly against the bed. His black leather pants start +

to tighten, and he realises too late that he should've probably taken those off. His ass begins filling out, pushing against the fabric as it stretches to accompany his growth. His hands fly down to his ass, grabbing at it as it fattens, spilling through his fingers. It feels...+

It feels impossibly /good/, and Izuku starts to grind his ass back against his hands as he gets bigger and bigger. Even if he had both hands against one cheek, he wouldn't be able to contain his ass, and he moans as it bubbles out.
"K-Kacchan," Izuku breathes, loving the way +

his ass remains round and firm as it widens, desperately straining the fabric that's struggling to contain it. Each cheek is bigger than his /head/ now, but he knows he's going to get much bigger than he is. The thought drenches his leather jeans in slick, giving them a shiny +

gloss. Izuku leans forward, his ass pushing outwards as it gets bigger and fatter still. His jeans can't hold it anymore: he rips small holes all over his jeans as his ass surges past, more and more tantalising skin being put on display as he continues to grow. He cries out as +

his jeans finally give out, his ass expanding more steadily now that it isn't restrained by the shiny fabric. His thong is practically swallowed by his ass, his cheeks shiny from the slick pumping out of his hole. His face is flushed as he pulls his small cocklet out and starts +

jerking himself desperately. His ass bounces with the movement as it grows more and more, filling out the bed as he leans further forward to give it more space. It's closer to the size Kacchan wants now, and knowing that he's turning his Alpha on by getting bigger just makes him+

stroke his leaking cock harder. His ass presses into the mattress as it gets heavier and rounder, but it's starting to slow down now, almost at the size his Alpha wants. Izuku slaps his ass, watching as it ripples. He grabs a handful again, but this time his hand doesn't even +

cover a fraction of it, practically disappearing against his generous rear. He ruts against the bed, panting as the lust takes over his mind. The expansion slows to a stop, but Izuku wants to cum, he /needs/ to cum, he-
And then Kacchan is bursting into the room, on top of him +

in a second. Izuku spreads his ass cheeks, falling forward and presenting to his Alpha as he whimpers, "K-Kacchan, I'm so /biiig/, just the way you like it, so please please /please/ fuck me, Kacchan, I need it, I need your knot, I need you /inside/ me-/ohhhh yesss/!"
Kacchan +

steadies one hand against Izuku's big, fat ass, the other gripping his dick as he begins sliding into Izuku's sloppy, dripping hole. And /ohhhh/, Kacchan's dick is so /thick/, the perfect fit for his huge, slutty ass.
"Fuck, so fucking hot, so fucking perfect, fuuck," Kacchan +

praises, smacking his ass as he pushes in /hard/, bottoming out and making Izuku's ass jiggle from the impact. "You're so fucking big, just the way I like it, Omega. You did so fucking good, taking it like that, I'm gonna give you what you want now, I fucking promise."
"Yes, +

yes, yesss," Izuku whines, eyes already rolling back as Kacchan starts to thrust in and out. "Fuck me, fill my big fat ass, /breed/ me Kacchan, I want it so badly!"
Kacchan picks up the pace, moving his hips back before he snaps them back forward, fucking in and out of Izuku's +

ass it jiggles wildly. Of /course/ it does. It's huge, each cheek maybe three times the size of Kacchan's head, and it seems even bigger against Izuku's otherwise tiny little Omega body as Kacchan pounds him into the mattress.
"Mm, fuck, just look at it /move/," Kacchan marvels,+

abusing his prostate over and over and over as he drives into him /deeper/ and /harder/ and /faster/. Izuku can't even respond, mouth helplessly sliding open as slutty sounds escape him. His tongue lolls out, his expression the perfect ahegao as his Alpha, /his/ Alpha, wrecks +

him. Kacchan knot is starting to catch on the rim of Izuku's tight hole, and he takes the edges of the jeans, ripping them even further to expose more of Izuku's sizeable ass as they both get closer and closer to orgasming. Izuku's dick brushes against the soft mattress, and he +

moans louder and louder until he's practically wailing, tears spilling down his cheeks as Kacchan finally, /finally/ pops his knot fully, stuffing Izuku's ass full of cock and filling Izuku's belly up with cum.
"K-K-Kacchan!" Izuku screams, legs giving out from the pleasure and +

weight as he cums, small dick spurting cum all over the mattress. Kacchan slumps forward over him, squishing Izuku's fat ass against his body him as he nuzzles his head against Izuku's scent gland. He licks and laps at it, and Izuku hums.
"Can I?" he whispers, pressing kisses +

against it.
"Please," Izuku sighs happily, baring his neck. Kacchan cups the Omega's face in his hand, tilting it towards him so that he can look him in the eye as he says:
"I love you, Izuku."
Izuku's heart flutters.
"I love you too, Katsuki."
The bite is like ecstasy, a +

different high to his orgasm. He adores it more than the mind-blowing sex.
***
(Katsuki's delighted to show Izuku off to all the other Alphas, and Izuku loves how possessive Katsuki is over him when other Alphas drool over him- they both love his body, and /each other/.)
END.

Fuck you, tweet limit I'm so happy to be writing again, and this is the best way to get back into it! I absolutely do not apologise for making Izuku's ass that big; that's the whole kink If you stan big ass, please consider supporting my writing! http://ko-fi.com/lemonaestheticc 

ALSO: Thank you so much to the person who donated anonymously for this. The message was along the lines of "pick the one you're most looking forward to and write it <3" and I kid you not, that made my whole month, I really appreciate it