Kirishima was practicing on Katsuki to confess to Mina,and, well..Izuku just watched from afar and misunderstood the situation.

”You better have a good reason why you want to talk.” Katsuki says as he steps into Izuku's dorm.

Izuku simply pins Katsuki to the wall. ”What the fuck,nerd?” Katsuki exclaims.

”I'm not in the mood for your yelling, Katsuki.” Izuku says, oddly calmly. Too calmly.

”Why was Kirishima hugging you and giving you a rose today?” Izuku asks forwardly.

Katsuki snickers at the obvious jealousy on Izuku's face. ”He was asking for help to ask Raccoon Eyes out,and i let him practice using me.”

Izuku's firm expression immediately falters.

”I'm so sorry for overreacting Kacchan,i just felt jealous for some reason. Sorry if i made you uncomfortable i—”

His yapping session is interrupted by Katsuki pulling him into a kiss.