Souta visits his wife's family home for the first time in a long while and reunites with his mother-in-law, Chisato. He is confused by her sex appeal, which is not found in his young wife. So, when he goes to take a bath by himself to cool his head, Chisato suddenly appears and washes his back, saying, "I'll wash your back. I'm your son, so don't be shy." Souta is in a state of arousal, and when she washes his back as well, he gets an erection...