The patron-submitted idea that will become a Gumroad audio next month is... (Patreon)

Little brother sleepwalks into his big sister's room. At first he is only sleeping next to her but soon he takes advantage of his sister. She tries to fight him off but he is just too strong. She tries to talk to him about it the next day but he has no memory of the previous night. It becomes a regular occurrence. Tonight he doesn't pull out and pumps multiple loads of cum into her tight pussy!