Weekend only, couple exchanges: Night when a wife is embraced by someone else

In her fourth year of marriage, Nanami's husband Koji, has just become independent and is busy with work, and perhaps due to the rut, the couple has stopped talking recently. In contrast to the two, Hibiki moved into the room across from her, and she was close to her husband, and every time she saw the couple, Nanami was envious of her. Eventually, Hibiki learns about Nanami and her friends' cold marriage relationship, and invites Nanami and Koji to their home and proposes a marriage exchange only on the weekend...