Aina discovers that her older sister Rena has become her brother Shota’s sex toy. Unable to bear it, she sneaks into Shota’s room at night…!? Using the lewd techniques she learned by secretly watching him with Rena, Aina tries to take the initiative—but as she experiences pleasure, Aina’s arousal only grows! Along with her sister Rena, Aina also gradually undergoes training and becomes a sex slave…!
