Bad Teacher's Equation(1993)

Kusatta Kyoushi no Houteishiki

Atsushi Arisawa enrolled at Jougaouka High School in order to reunite with his childhood crush; Ma-chan, who is now the school's nurse. Strangely, Ma-chan's previously sweet personality seems to have radically changed beyond all recognition. Things are even more complicated when Atsushi's friend, Kouji, tries to put the moves on him. Atsushi just wants Ma-chan though, so perhaps if he gets to know the new, adult Ma-chan, he will find he is not so bad after all. But wait a minute...his name isn't Masami, but Masayoshi?

(Source: Juné)