Perhaps dig into the Norse Religion and see how many comparisons you dig up. Last city = Valhalla Ghosts = Valkries Guardians = Einherjar Our galaxy = Vígríðr Tricorn = wolf = Fenrir = Destruction of the Traveler Traveler was one of the names for Odin. You're brought back to prepare for and fight a battle in the field of Vígríðr, which will result in countless death but ultimately save the world as we know it.