Thread by @lemonaestheticc

cw: ass expansion
Izuku's patrolling with Katsuki, tracking down a villain with an unknown Quirk, when he gets hit by something. It's not something /tangible/, but he can feel it tingling throughout his body. He knows instantly that he's been hit by a Quirk, and he yells out to +

Katsuki to tell him as much.
"Keep pursuing the villain, Kacchan!" Izuku calls, when suddenly the sensation gathers in his ass, making him jolt. He glances down at his ass, clad in his hero costume - an altered version that cuts off mid-thigh to allow his legs more freedom and +

for his enforced boots to wrap around him just under his knees. He watches as the material over his ass starts to stretch, he /feels/ the hot sensation in his ass start to get more intense. "W-What is this!?"
Kacchan should've run off by now, but it's too late to catch up, and +

he looks like he's been caught utterly off-guard by-by /this/. Izuku watches in flushed horror as his ass /grows/, pushing out and forcing him to lean against a wall as it continues to get bigger and bigger. He moans as it strains against the fabric, too big for his hands to +

hold it. He tries to push at his ass, trying to stop it from growing, but the growth only speeds /up/, bubbling through his fingers and continuing to get bigger despite his efforts to /stop it/. Izuku's helpless to do anything but /watch/ and brace his arched body against the +

wall as his ass gets rounder and fatter, the seams of his costume straining further and further. The shorts ride up his thickening ass as the tingling grows even more intense, and Izuku cries out when the the seams start to rip, his fattening ass pushing out between the torn +

fabric.
"D-Deku?" Kacchan manages as Izuku's ass expands more and more, the fabric tearing under the strain of his big ass until only a few threads are holding together his struggling costume. His ass is so /big/, bigger than he could've ever imagined, and yet it's still +

/growing/, jiggling as it gets fatter. The heat in his ass is spreading too, making Izuku feel /aroused/, and when he tries to respond to Kacchan, all that comes out is yet another helpless moan. He arches his body out further, his legs trembling under the weight of his growing+

ass. His mind should be racing with thoughts of how this is possible, what the Quirk might be, if he can undo it at all, but instead all he can think about is how /big/ his ass is getting as it gets heavier and heavier, bulging out between the stray threads that are still +

digging into his fat ass. His face flushes deeper as he slowly sinks to his knees under the weight of his expanding ass, and he bites his lip as he watches it grow bigger and fatter and rounder. He can see the way Kacchan is looking at him, jaw-slacked as Izuku's ass jiggles +

more and more, each surge of expansion keeping it moving like he's shaking his ass or something. He feels it before he hears it - the final threads still clinging to his generous ass starting to snap one by one. Each time a thread snaps, his costume tearing under the weight and +

sheer size of his ass, the pace of expansion quickens, his ass getting bigger and fatter /right in front of Kacchan/ without any sign of slowing down. His ass is /huge/ now, enough for Kacchan to bury his face in and-
Wait, where did that thought come from? Izuku bites his lip, +

trying to keep his arousal to himself even as he starts to roll his hips, making his ass jiggle and shake even more as it grows and grows and /grows/.
"W-What's going on?" he pants as his ass surges outwards, exposing his thick thighs and sensitive dick to the air as the fabric +

gives away entirely. He can't deny it anymore; it feels /so good/ to watch his ass getting so, so /big/, and while he knows it's a side effect of the Quirk, he can't help but want /more/. He'll be too far gone soon, so in a final ditch attempt, he cries: "K-Kacchan! Help me!"
***

I wrote this lil horny thread to cheer myself up 🥺👉👈 I'm trying to be less embarrassed about my kinks, so if this isn't your thing, plz don't make fun of it ;-;
Anyway, this was based on the art that Anon drew for me, bc ass expansion is delicious 🤤💕
ko-fi.com/lemonaestheticc