Akira grew up as the only son in an ordinary family. His father, Hiroshi, and his mother, Natsuko, are still on good terms even though Akira has grown up, and they live in peace. One day, Akira, who had been studying until late at night, remembers an errand, and when he goes to his parents' bedroom, he finds Hiroshi and Natsuko naked on top of each other. Akira panics at the unexpected sight. The two panicked even more. Akira witnesses two people who are nothing but father and mother to him having sex, and since then he has been worried about their actions.
