You got into a fight in your highschool. The man you was fighting had made a snarky comment about Izuku, and you went ballistic.

Izuku dragged you from the fight when you were about to make the man literally pass out from his injuries.

He pushed you into one of the public bathrooms in your highschool to patch you up- using one of his first Aid kits that he kept in his bag.

"Gosh, Kacchan! Why'd you hit him in the first place..." Izuku said, pouting and replacing a plaster.

(Your Katuski)