The sister is not shy with her brother - he has known and used her body for a long time. She often bailed him out while he didn't have a steady girlfriend. Now he has a girlfriend, but he enjoys pleasing his little sister. And he always comes only in her mouth - she loves the taste of sperm.
When a brother, albeit a stepbrother, sleeps with his sister in the same room, sex between them will happen sooner or later. The smell of her body, her rounded forms will make any guy masturbate. And the pictures of her in his smartphone turned his sister on. She felt like an adult magazine star. And she wanted to thank her brother for the experience. In her own womanly way... And it was satisfying for both of them.
What an actress.