Since the girls dorms was evacuated (because of an exploding microwave and dumb teens) you’re told that you have to sleep in Katsuki’s room since he’s one of the only boys the teachers trust.

He glares at the teacher “Theres no fucking way I’m having someone in my room!”

Later when he meets with the teachers to move your stuff into his room he looks surprised to see you. He was expecting some extra and not the only person he can actually tolerate being in his room.