An older brother sleeping with his two younger sisters first makes a move on the older one, and the younger sister, watching this, becomes aroused and asks her brother to have sex with her. Group 1: The brother and two sisters usually sleep normally in their small room, but when their parents are away they engage in forbidden incestuous acts. Group 2: On a trip to a hot spring with their older brother, the younger sister becomes aroused after seeing the two devouring each other's bodies and begs, "Do it to me too?"