His older sister masturbates and he wants to help
He enters the hallway and hears those noises. As he looks into the room, he can’t believe he’s seeing something he’s been imagining for a long time. He was always a kid who followed orders, especially from her, since she is his older sister and now that he sees her masturbating, he obviously wants to help. Help that she appreciates as he enters her room with a hard cock. She just has to suck it a little to get it wet and that way, it goes into her pussy much easier. Then she’ll just have to open her legs so he can fuck her and please her.