After losing her husband, Rieko lived alone until her daughter and son-in-law returned home after two years. The couple planned to stay with her for a while. Though they had a strong relationship and the son-in-law was generally satisfied with married life, a quiet dissatisfaction began to grow within him at night. One evening, while heading to the bathroom, he heard strange sounds and discovered Rieko masturbating. Excited by the sight, he tried to initiate sex with his wife, but she refused, saying she was holding back due to having a young child. His frustration intensified. The next day, while his wife slept, the son-in-law approached Rieko and forcefully made advances, whispering, "You want this too, don't you, Mom?" Though she initially resisted, Rieko gradually gave in as her emotions wavered, leading them into a forbidden relationship.