“I want you to fuck me like my big sis!” Aina discovers that her older sister Rena has become her brother Shouta’s sex pet. Unable to stand Reina monopolizing Shouta any longer, Aina finally sneaks into Shouta’s room at night…!? Using the techniques she learned by secretly watching him with Rena, she tries to take the lead — but as she experiences the real pleasure, Aina’s arousal only keeps growing! Alongside her sister Reina, Aina too is gradually trained and broken in…!