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

It's been a week since my wife got pregnant and went back to her hometown. Kentaro is enjoying living alone for the first time in a while, but he is beginning to feel lonely in the quiet, unpopular home. At that moment, my sister-in-law, Mio, came to check on her. She is unable to endure the loneliness, so she welcomes Mio, but Mio's true purpose is to relieve her frustration with Kentaro. Kentaro has been completely deceived and is taking a bath with care. Then Mio came in, "I'll let my back flow."