Living together with my girlfriend, I was surprised one day when her older sister, Marin, suddenly showed up and announced she'd be staying at my place for a week. Before long, I found myself constantly exposed to unintentional upskirts and cleavage flashes from her, making it harder and harder to suppress my arousal. Eventually, unable to hold back any longer, I gave in and had secret, out-of-control sex with her behind my girlfriend's back. Then Marin said, "Oh my, I can totally feel my boyfriend's intense gaze..."—and the woman who once seemed unapproachable revealed an unexpectedly erotic body and teasing nature, driving me to full erection every time.