The sister's eyes widen as she sees her brother's erection growing in the shower. She hesitates, then reaches out, wrapping her soapy hand around his shaft. He gasps, bucking into her touch. She strokes him, her other hand cupping his balls, before dropping to her knees, taking him into her mouth. He grips her hair, fucking her face as the water pours down their bodies, their moans echoing off the tiled walls.