Sanity is Quite Simply Overrated

Earth died, muggles and magicals had warred and damned themselves into oblivion. The only survivor was the less than sane Harry Potter. Eventually he stumbles upon the Veil of Death, on a whim he decides to walk through and soon awakens in his cupboard under the stairs as one Harriet Potter. The Marauders shall ride again, led by a not quite all there witch. (Black Family revival)