mother-in-law and sister-in-law

Sawako, who broke up with her husband a few years ago, remarried her current husband and took their daughter Naomi with her. Her husband also has a 20-year-old son, Keisuke, and their remarried life continued to be peaceful for a while... One day, my brother-in-law Tatsuya comes to my house. That night, Sawako, who was worried about Tatsuya, who is the complete opposite of her husband, commits adultery with Tatsuya in the next room where her husband sleeps. From that day forward, the gears of the Kusunoki family gradually go awry. Meanwhile, Keisuke, who was the only one watching his family fall apart, approaches Sawako...