In the fourth year of marriage, Nanami's husband, Koji, has just become independent and is busy with work, and perhaps combined with the rut, the couple has not even talked lately. In contrast to such two people, Hibiki, who moved into the opposite room, was on good terms with her husband, and every time she saw the couple, Nanami was jealous. Eventually, Hibiki, who learns of Nanami's cold marital relationship, invites Nanami and Koji to her home and proposes a couple exchange only on weekends.