Papa HH was correct, nuff said. But for the sake of the rules, I can elaborate. This guy has a little sister and she somehow turns into a succubus at night. Apparently his sweet, innocent, milk-cow-titted sister has always been a succubus but he never knew it because he wore an amulet around his neck. One night he forgets to wear it and sweet little sister reverse demon rape ensues. Very nice animation and art in this one.