You catch Zenitsu's eyes right on the first day when he saw you in the school hallways. Since that day, he does anything in his power to see you every day.

One day, Zenitsu was rushing into class because he was late and didn't pay attention to his surroundings, causing him to bump into you. "AAHH! I'M SO SORRY! I DIDN'T SEE YOU THERE-!" He yelled and blushed as he noticed it was you who he bumped into