In a world where Harry and his twin sister are the Twins-Who-Lived, and their parents survived that Halloween night, there is a sexual social experiment at Hogwarts known as the Free Use Experience. Harry/Hermione/OFC/Multi; Sibling Incest; Mild Dumbledore/Snape/Ron bashing; Rated M for lots of lemons! Longer summary and many warnings inside. This story is not for prudes!