An older sister witnesses her younger brother masturbating while watching an erotic video. At first the younger brother is shocked, but as he starts watching the porn video with his older sister, who is very interested in it, his older sister's breathing gradually becomes heavier. Unable to calm down, the older sister goes into the bathroom while her younger brother is taking a bath, and becomes even more excited when she sees his penis, offering to help him masturbate. The younger brother also becomes excited as his penis is touched, and finally he can't hold back...