The brother, driven by primal urges, can't resist the allure of his sister's ass any longer. He grabs her hips, pulling her towards him, his cock pressing against her ass. She moans, grinding against him, her body aching for more. He slips a hand around to her front, fingers finding her wet pussy, slipping inside. She gasps, her body tensing as he fucks her with his fingers, his other hand squeezing her ass. He can't take it anymore, pulling out his cock and pushing it against her asshole. She pushes back, taking him in, and they both groan in pleasure as he begins to fuck his sister's tight ass.