The tight space forces them together, their bodies rubbing, slipping against each other. The sister, her inhibitions lowered by the hot water and steam, takes her brother's cock in hand, feeling its hardness, its heat. She guides him to her entrance, feeling the tip push against her, stretching her. She's never felt so full, so naughty. Their eyes meet, and they know there's no turning back. The water continues to pour over them, washing away their guilt, their shame, as they give in to their forbidden desire.