The teacher is a grouch, an asshole, and is in psychological agony as he is tormented with loneliness. Unfortunately, the story doesn't do much at all to explain why he is the way he is. The student is an angel. Gentle, sensitive, even willing to be groped by the teacher from time to time. Why? Same as the MC, none of it is explained. None! Does the student grow? Nope. Does the teacher grow? You can say that if you loosely define the word "grow". He changes, he mellows down (barely) because of the girl's company I guess. He also goes into some kind of mission ofreading books on learning how to be kind.

All in all, it's like watching some random macabre theater. You hope something in the end clarifies everything, but nothing is clarified except for some vague declaration that anyone can be kind, even someone as empty as him. The ending of this series is like that ending declaration: weak and vague.