The brother's eyes widen as he catches his sister bent over, her ass in the air, fingers buried deep in her tight anal hole. She moans, not realizing he's there, her body writhing with pleasure. He can't help but join her, his cock throbbing as he watches her stretch herself open. He lubes up, his fingers replacing hers, pushing deeper, stretching her wider. She gasps, her body tensing as he replaces his fingers with his thick cock, her ass stretching to accommodate him as he plunges in, filling her completely.