One day, the Sasaki couple accidentally meet Ataru, one of the husband's students. Ataru, who has secretly had feelings for Aki for a long time, is invited to their home, but drops his keys when he leaves... The next day, when Ataru comes to collect the key, all the pent-up emotions explode, and he pushes Aki down. Aki's body refuses to listen to Ataru's relentless thrusts and she accepts. From that day on, Aki refuses Ataru's persistent requests for a relationship, but the throbbing of her body shakes her mind deeply...