Bondage Group Assault.

A high school student living with his older brother and his wife. A timid boy who always masturbates thinking about his brother's wife. His older brother and his wife always seem to get along well. His brother's wife is elegant and beautiful. However, when his brother is on a business trip to a local city, he keeps a mistress. His brother and his mistress also seem to get along well. A couple lives next to the mistress' room. They also seem to get along well. However, contrary to this outward appearance, the characters' hidden sexual desires lie hidden.