Ruka and Reiko spend a cozy time with their neighbor's mom friends. The two of them become very interested in the one word that the mom friend casually said, "Ryoichi (son)'s dick is about the size of an old telephone receiver." Furthermore, the mom friend needed to return to her parents' house and was worried about leaving Ryoichi at home. The two of them, wanting to see Ryoichi's big dick, take care of Ryoichi for a week, thinking that they should help each other out when they're in trouble. A few days later, that day finally came. From that day on, a week of obscene sex like a rosary chain began...