Even though my relationship with my girlfriend is already on the verge of collapse, I find myself unable to suppress my uncontrollable urges. The reason behind this is her younger sister, Mayu. She's always teasing and tempting me in an aggressive manner. With her cute smile and straightforward gaze, she's shaking my heart. We deepen our relationship as she suddenly gives me a blowjob in the hallway or surprises me with a titty fuck in the bathroom. Eventually, we end up having secret sex in the bedroom while her sister is sleeping. I know this illicit relationship won't last forever. However, I'm beyond self-control now. As I imagine what the future holds for my relationship with my fiancée's younger sister, my heart can't be stopped anymore.