Nishida, a newly appointed teacher, arrives at a school in a depopulated area with only one class. The principal of this school is plotting to get students into college through the back door. Nishida, with his strong sense of justice, confronts the principal, stating that he will not rely on the back door and will instead advance to college on his own. Nishida begins his lesson by using his own anus as a subject, hoping to help his students understand the importance of learning. He carefully teaches the students how anus works, offering rewards to those who improve their grades. After reconciling with the principal and successfully expanding his anus, he engages in a highly challenging public double penetration, urging them to never give up.