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

Atsushi takes advantage of her wife, who has been pregnant and about to give birth, returning to her parents' house, enjoying life alone, just like she was single. Without any notice, his wife's sister, Kiriko, came to visit him, thinking that she was in trouble on her own, so she came to check on her. She ignored Atsushi, who said that it was okay because that was not the case, and forced her to stay. Then, when Atsushi was taking a bath, she rinsed her back and Kiriko appeared in the bathhouse and was completely naked...