Kazushi, a university student living alone, is troubled by the presence of two childhood friends, sisters, who hang out all the time at his apartment. The cheeky older sister, Ayane, and the laid-back younger sister, Kotone. With the two always around, Kazushi has been semi-forced into a life of abstinence for a long time... One day, a trivial argument leads Kazushi to take a bath with the sisters in the apartment's tiny bathroom. Even though he is still wearing his swimsuit, the soft touch of them clinging to his body makes Kazushi's reason waver.