The daughter and son-in-law wanted to save money to buy a house, so they went to live at their mother-in-law's house. Reiko used to work as a photo model before, and she had no idea that her son-in-law was a fan of hers. One day, Reiko accidentally discovered her son-in-law was watching a porn movie with an actress very similar to her, surrounded by photos of when she was a model. He used her photo to masturbate! Reiko couldn't take her eyes off her son-in-law's huge cock. It turned out that because the cock was so big it caused Reiko's daughter pain. It had been a long time since her son-in-law had had sex so he had to "deal with it" alone. Feeling sorry for her son-in-law, Reiko decided to offer her daughter to "take care" of his big cock. Reiko's invitation, combined with having endured it for so long, made him unable to resist anymore. From then on, the two continued to secretly fuck each other every chance they had, secretly maintaining this wrong relationship...