Although her relationship with her husband is happy, Umi is unable to have children and her days of despair grow. One day, her brother-in-law Kyoichi comes to her house for a memorial service... Kyoichi, who has a strong libido and loves women, relentlessly taps into the carnal desires hidden deep within her. "I was just carried away..." Umi tells herself, and they end up having a one-time affair. However, her pleasure is quickly overwritten by his relentless caresses, which are incomparable to those of her husband, and the stimulation of his penis, which penetrates all the way to her brain. And before she knows it, Umi has fallen victim to a secret affair with her brother-in-law...