Three years into her marriage, Yayoi's husband gradually stops initiating sex, leaving her anxious that she has lost her appeal as a woman. Then her brother-in-law Tomohiro, an adult studying to retake his entrance exams, moves in for a month so he can attend prep school. As Yayoi treats him with warmth and kindness, Tomohiro becomes increasingly attracted to his sister-in-law, and his desire begins threatening her marriage.