The Kato family, consisting of the wife, her husband, and her father-in-law, live happily together. However, she is troubled by the fact that she has not been blessed with children, and consults her father-in-law. The father-in-law is also unable to find an answer, but the wife, thinking that her husband has many siblings and that the father-in-law's sperm is strong, asks the father-in-law to inseminate her. At first, she thinks it is just business, but gradually she becomes addicted to sex with her father-in-law...