While reporting on a recently formed volcanic island, journalist Iwakura finds a stranded young man with no memories. News of the incident catches the attention of a mysterious person called Rush, who tracks down the amnesiac and explains to him the truth about his identity. The young man is named Mars and, like Rush, he is not originally from Earth. Mars was dispatched with one mission: to command a tremendously powerful robot named Gaia to destroy Earth when it becomes clear that humans are attempting to extend their influence into outer space. As a precaution, Gaia is programmed to self-destruct, taking the planet along with it, in the event that Mars dies. In light of Mars' amnesia, Rush agrees to give him 10 days to study Earth's history and decide his course of action. Mars must now choose whether to follow through with his duty or fight to save humanity.