A guy worked far away from home and today he returned to his hometown to comfort his mother for the 17th time. At home he met Riho Fujimori, his older sister, who had gone through many bad marriages. After dinner, his father suddenly announced that he was not the family's biological son, shocking him greatly. But after that shock, he calmed down and thought that he could approach his sister Riho without barriers anymore. When he meets a single and lonely woman, it's easy for him to seduce her. They secretly made love to each other many times in the house. Even though they were not related by blood, the act was still incestuous.