Himitsukichi ni Aijin

Synopsis

An invitation to a secret base that suddenly arrived to Tetsuji, who is called "Manbo-Sensei" by the students. I was suspicious, but when I visited, there was a strange young man there. "I will answer the question if you will make love with me one time" The purpose of the invitee who boldly invites me is...!? Note: Chapter count includes an extra.