I'll Educate You on Everything

Chiaki left his phone at school, so he goes back that evening to retrieve it. While he's there, he hears soft moaning coming from a nearby room and decides to take a look, only to find Mr. Chiba, the math teacher, taking it from another man... Despite being geeky, all the girls love Mr. Chiba, who in turn constantly nags Chiaki about getting more...