After a fight with his wife, his wife went back to her parents' house. While Koichi was spending the day alone, his sister-in-law Nao came to visit him. He was grateful to her for giving him advice on how to make up. Nao's real target was Koichi's body. Taking advantage of her sister's absence, she repeatedly teases him with provocative poses, and while he was taking a bath, she washed his back and then barged into the bathroom. Koichi was shown her sexy body and although he verbally rejected her, Nao noticed that his lower body was responding well...