In the cramped, dimly lit gym, sister and brother engage in an unusual form of cardio. She hops onto the stationary bike, her tiny spandex shorts barely covering her round ass. He stands behind her, mimicking the motion on an imaginary bike, his gaze locked on her wet, glistening pussy. As she pedals faster, her breath hitches, and he can't help but reach out, brushing her clit with his fingers. She gasps, pushing back into his touch, their bodies moving in sync, fucking without penetration.