The Koayakawa family, consisting of a wife, her husband, and his father, live harmoniously together. However, they are troubled by their inability to have children and consult the father-in-law about it. Although the father-in-law couldn't find an answer either, the wife, noting that her husband has many brothers, thinks that perhaps the father-in-law's sperm is very potent. She ends up asking him for insemination. What started as a business-like arrangement gradually turns into an obsession with sex for the wife. They agree to end their relationship once she gets pregnant, and when pregnancy is confirmed, their relationship comes to an end. However, after giving birth, they can no longer hold back and resume insemination intercourse…
