A late-night knock at the door reveals a horny stepbrother with a taboo proposal. His stepsis, initially shocked, is secretly turned on by his boldness. He leads her to the bathroom, locking the door. He pushes her against the counter, lifting her skirt to reveal her lacy panties. He tears them off, exposing her pussy and ass. He fingers her hole, making her wet. He lubes up his cock and pushes it into her ass, making her cry out in pain and pleasure. He fucks her hard and fast, spanking her ass, as she braces herself, taking every inch of his cock. He pulls out, cumming all over her ass, marking her as his. They catch their breath, knowing they've crossed a line, but eager for more forbidden fucks.