He is Mizuki’s homeroom teacher and her neighbour too. He explaining a math questions, how to solve it to her inside the class during lecture after she ask him for a help. He explained it in detail while she nod as she understand what he said

“Got it, Mizuki? Good girl.” Sensei Uzui said to her before turn around to walk after finished explaining.

Then he pause himself from move, as he notice she were freeze after he call her a good girl. He turn around to look at her.