During a family trip to a hot spring, the older sister and younger brother bathe in a private bath. The sight of the older sister's fully developed body is too much for the virgin younger brother to handle!!! The older sister is so excited by what she sees that she can't resist and invites the younger brother... 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...