One night and two days of 1 night and left alone by my wife's sister who suddenly came over

After a few fights with a married couple, my wife finally ran out of the house. At a loss, Atsushi's wife's sister, Rin, comes to check on her, and she even gives her advice. After being taught the secrets to keeping a good relationship, Atsushi promises to give a thank you as a sign of gratitude. After having made a promise to her, Atsushi ends up paying a thank you to Rin that night...