Koichi was left alone after a marital argument caused his wife to return to her parents' home. During this time, his sister-in-law Nao suddenly showed up, claiming she had come to offer advice on reconciling. Grateful for her support, Koichi welcomed her warmly. However, Nao's true intention was to seduce him. Taking advantage of her younger sister's absence, she began acting strangely, teasing and provoking him repeatedly. While he was bathing, she barged into the bathroom under the pretense of washing his back, flaunting her sexy body. Though Koichi kept verbally refusing, his physical reaction was obvious. Nao noticed it all…