Makoto-sensei no Junan

Hiiragi Makoto is a male teacher of Seigunkan Academy. One day he got rejected by Ichinosei Haruka after confessing his love. In deep shock, he has an accident and undergoes an operation at the hospital.
"Oh how I wish I was born differently" he says to himself. And thus an unexpected Earth-shattering change occurs.
"Where is this place? Why do I have boobs?"
He continues teaching as a career now as a female and spends a 7-day trial in the usual all-male section of the school.
”I must definitely protect my virginity and pride."

[Translated from the official website]