History has a way of repeating itself. As Erebus, he had been the villain; as Thanatos, he was Death's charismatic right-hand; and as Percy, he was the lauded hero... until the gods threw him into Tartarus. When Gaea ascends in power, the Olympians desperately seek help in the form of an unknown entity—one that knows them better than they know themselves. Primordial-Percy. P/R, AU.