Ryuudouji Shimon no Inbou

The protagonist's name is Ryuudouji Shimon, who lives in a shabby suburban apartment hiding from the society. It's been four years since he left his teaching career for some reason.

One day a letter arrives at his door. It is a teaching offer from a prestigious girls' school that is famous in Tokyo.

Despite doubts and concerns, such an opportunity is hard to turn down, so he steps into the girls' school.