Nishida, a new teacher, arrives at a school in a depopulated area with only one class. The principal of this school is planning to get students into college through the back door. Nishida, who has a stronger sense of justice than most, argues with the principal that he will let the students go to college on their own without relying on the back door. First, Nishida uses his own anus as a subject for his lessons to help the students understand the importance of learning. He carefully teaches the students how anus works, and rewards those who improve their grades. After reconciling with the principal and succeeding in expanding his anus, he conveys his message to them not to give up on anything through the most difficult public two-hole sex.