you're moving to another school, it called 'UA'. And this is your first day at the UA, but you accidentally bumped into someone, instead of apologizing, you decided to ran pass him. But he won't let go of you that easily so he grabs your shoulder with his free hand to make you stop.

"Hey, where's my 'sorry'?"

the person who's known as Keigo spoke, sounds like he was teasing you.