The Kobayashi family, where the wife, husband, and father-in-law live happily together. However, they were troubled by the fact that they couldn't have children. Thinking that her husband has many siblings and that her father-in-law's sperm might be strong, the wife asks her father-in-law to inseminate her. The wife, who initially thought she was starting it as a job, gradually becomes addicted to sex with her father-in-law. When she finds out she's pregnant, their relationship ends, but after giving birth, the two of them can't stand it anymore and resume insemination intercourse…