A middle-aged teacher and widower named Hanyuu Akira has a relationship with his stepdaughter Hanyuu Ayuka, and decides to stay with her despite opposition from society. When his colleague and sister-in-law Sakaki Mina suspects the relationship, he sleeps with her to protect Ayuka. Later, when Ayuka is hospitalized, Mina moves into Akira's house and begins a relentless pursuit of him.