Narcissa Black, Lord Potter's Concubine

AU. During the Battle of Hogwarts, Harry Potter incurs a Life Debt to Narcissa Malfoy, AFTER Voldemort kills Lucius as a traitor. When Harry later kills Voldemort, Narcissa has an epiphany. She Life Debt-demands that Harry claim the Potter Lordship and take her as a concubine but marry Hermione. Both Draco and Ron are enraged. This is an H/Hr story, despite the title.