Katsuki being jealous as fuck even though he's emotionally constipated and suspecting that there's something between Kiri and Deku, so he starts spying and asking questions. Both of them seem very uncomfortable at his questions, because little does he know, there /is/ something +

going on between them, but not what Katsuki thinks. Kiri and Deku are friends with benefits, because both of them are too scared of being rejected by the people they actually like. Izuku's got curly hair and a big ass like Mina, and Kiri's as tall and muscular as Katsuki, so +

they make it work. Plus, they're good friends anyway, and the both of them have mind-blowing sex. Deku's eyes will flutter shut as he imagines Katsuki spanking his fat ass as he fucks him mercilessly, and Kiri will imagine sinking his hands into Mina's ass and threading his +

fingers through her soft hair as he fucks her. But obviously, Katsuki is unaware of this, and he's started to grow /really/ suspicious of the two of them sneaking around. He thinks he heard something in the showers once, and he regrets not yanking back the curtains to check, but+

he can't dwell on that. He has to get to the bottom of this, because there's no chance in hell that he's going to confess to Deku only to be shot down. And because Kiri's involved, Katsuki gets /Mina/ involved, because although she might not talk about it that much (she loves +

gossip, but she's strangely quiet about her own love life), Katsuki knows for a fact that she's whipped for Kiri. So all it takes is a, "y'know, I think Deku and Shitty Hair might be fucking around" to get her invested. Of course, she knows what Katsuki's doing, but she can't +

help but admit that it's intriguing, wanting to know the truth. And Katsuki works much better at figuring things out when Mina is there, and they finally catch the two having snuck off to Deku's room. They press their ears up against the door, their hearts sinking. Those are +

definitely moans. "We should just leave," Mina says, trying to stay cheery. "We have our answer."
"Oh hell no," Katsuki responds, and slams the door open. Deku is sprawled on the bed, face pressed against the pillow and hips hiked up, legs spread as he bounces his ass against +

Kiri's dick as Kiri grips his hips and fucks him harder. They freeze when the door opens, before scrabbling away from each other, Kiri lunging for his trousers and sliding them back on. Mina doesn't even say anything, letting out one choked laugh before leaving. Kiri runs after +

her, leaving Katsuki to stare at Deku's naked body.
"Kacchan, I-I can-" Deku tries, but Katsuki slams the door shut, marches up to him, and yanks his hips up into the same position, his clothed erection pressing between Deku's big, naked ass cheeks. Deku whines, pushing back +

against him.
"You're such a fucking whore," Katsuki growls, rutting back against him. He unbuckles his belt and pulls his cock out, before continuing the sliding motion against Deku's wet, dripping hole. "Bet you'd let anyone fuck your fat, slutty ass, huh?"
"N-No," Deku +

whimpers. "K-K-Kacchan, I was I-imagining /you/, K-Kiri was imagining /Mina/, w-we just couldn't-couldn't /tell/ you b-because-"
"You... wanted me?" Katsuki breathes, and Deku nods even as he rolls his hips back against Katsuki's thick cock.
"I-I /like/ you Kacchan, I want to be+

with y-you, b-but-ohhhh!"
Deku cries out, eyes rolling back as his mouth opens in a pant when Katsuki thrusts in roughly, Deku already stretched for him as he slaps Deku's big ass and builds a relentless pace. He spanks him over and over whilst he /pounds/ Deku into the mattress+

until Deku is wailing his name, tears streaming down his face. He slams against his prostate and Deku cums, and the feeling of Deku's hole clenching down on his thick cock has him cumming too, filling Deku up before collapsing next to him and whispering "mine" against his lips. +

Needless to say, when the four of them meet the next day, Katsuki's is hand possessively on Deku's ass, territorial bites and marks all over his body, and Kiri's arm is simply around Mina's hips. Mina grins and suggests a double date, and to that, there are no objections.
*

I wish I had more space, but I love possessive Katsuki, and friends with benefits, and krmn, so thank you so much for comm'ing this mini thread, @/SundayRain98! All comms are closed now, but if you'd like to support me, it would mean the world to me http://ko-fi.com/lemonaestheticc