Akitsu Masato, a seemingly ordinary student, has been unwittingly drawn into a government project called "Last Guardian." The project aims to prepare him to pilot the powerful "Zeorymer of the Heavens" robot, as a means to stop the global domination plans of the "Hau Dragon" organization. Masato discovers that his whole life has been a lie and that his "parents" raised him in exchange for compensation. The Hau Dragon built eight massive robots, each embodying a natural force, but only Zeorymer and Masato were kept by their maker, Kihara Masaki. The Hau Dragon has revived the seven remaining mechs and seeks the eighth, while Masato and Himuro must stop them but remain enshrouded in mystery.