During a family trip to a hot spring, the older sister and younger brother bathe in a private bath. Was the sight of the grown-up sister's naked body too much for the virgin younger brother? The older sister becomes excited by what she sees and can't resist, so she invites the younger brother over... At first, the younger brother is confused by the forbidden relationship, but his body is honest and he gets a rock hard erection, and in the end, he takes his virginity...