New Century Legend Mars

Mars is discovered on a forming volcanic island named Heisei, a man bearing no memory. In truth, he is an extraterrestrial operative sent to collect information to determine whether Earth should be destroyed. Accompanied by a colossal robot called Gaia and haunted by mysterious visions of a woman urging him to spare the world, Mars chooses to fight for Earth rather than annihilate it, even if that means confronting his own kind. Yet if Mars is killed, Gaia will detonate, destroying Earth in the blast.