In the 4th year of marriage, Koji, Nanami's husband, is both independent and busy with work, in addition to the constant changes, even the couple's recent relationship is no longer there. Unlike these two, Hibiki, who moved to the opposite room, had a good relationship with her husband, and Nanami would be jealous of him whenever he saw the couple. Finally, learning of Nanami's cold marital relationship, Hibiki invites Nanami and Koji to her house and proposes to exchange couples only on weekends.