Very much after the school festival and experiencing Katsuki to excellently kill it at playing the drums, everything went by normal. Until you felt like he was acting a bit off and probably more pissed then usual one day, and it raised your suspicions.

You might've not been a stupid bitch and decided to follow his path after school, watching him go to his dorm and closing the door a bit.

You peaked in, seeing Katsuki changed in a tank top and crushing a drumstick with his fist. He sighed as he slid on his headset, sitting down while he began to play the drums.

If not very loudly, at least loudly at the start; and a bit aggressive with his drumsticks. Can't he find any other object to hurt or some shit? But this is sick.