Atlantis

In the end of the Apocalypse War where Hell invaded Earth, Zero was unable to lock the hordes away all by himself, resulting in Demons invading the planet a few years after the Reset. During that very war, the amount of Mana that leaked into Earth's atmosphere was too great, and Heaven was unable to remove all of it before the Reset was complete. With those two factors combined, humanity had spent years being invaded by small groups of Demons all over the planet, but they had the means to defend themselves as well. Using their new Technomagic, humans built a flying island over the Atlantic ocean to be a base to their new global special operation force, the RFA. The island was named Atlantis, for irony's sake, and over the years became a symbol of hope for humanity, just as it grew in size, population, technology and functionality. To prevent easy tracking and therefore enemy attacks, Atlantis is always in movement, travaling all over the Atlantic ocean, just as it relies on a magical field for cover.