Sweet moaning voices coming from the next room… When I peeked in, there was my cute little sister masturbating!? I hadn't noticed it until now, but she's grown into a woman's body somehow… Gradually reaching climax while awkwardly fiddling with her pussy. The brother felt a sense of eroticism for his too defenseless little sister's masturbation… Even though he knows it's wrong, he can't resist and secretly sneaks up on his masturbating little sister.