Koyama, a serious man who runs a construction shop, has been married for 15 years and his children have grown up. Consequently, he has sex with his wife less often and only occasionally visits nearby brothels, starting to feel sexually unfulfilled. Around that time, Koyama's sister-in-law Rei, overwhelmed by child-rearing duties, found out about her husband's infidelity. To take some distance, she left her children with her parents and came to stay at Koyama's house. Seeing Rei express milk using a breast pump while talking to his wife, Koyama became aroused by her mature womanhood and started thinking about raping her…
