[F4M] The elder sister assists the younger brother.
While the younger brother is still learning about ladies, the older sister returns home for a holiday. He has been drawn to his elder sister for a while. They discuss school and how he is still learning, and she offers to assist him. Perhaps flaunts her body and offers him a bj before moving on to more. She might offer assistance if she notices him playing with himself or staring at her while she undresses, or she might pick on him before continuing.