(I've done it... ) The act of betrayal against his wife was committed by Yoshinori. All because of his sister-in-law, Yuu, who is in front of him. His wife went on a one-night, two-day trip, and Yoshinori was enjoying the freedom of living alone for the first time in a while. Then, suddenly, Yuu came to visit. In fact, Yuu had come to satisfy her desires with Yoshinori, but there's no way he would know that, so he let her in. Yoshinori, who had let his guard down because Yuu helped with the chores, went to take a bath, and then Yuu came in...
