Yûsha Raidîn

After a slumber of twelve millennia, the Demon Empire awakens to seize control of the Earth. Raideen, the giant robot-like protector of the lost continent of Mu, senses the evil presence and awakens within its golden pyramid. A young Japanese boy, Akira Hibiki, is alerted about the Demon Empire by a mysterious voice and rushes to the pyramid. It is soon revealed that Akira is a descendant of the ancient people of Mu who must help Raideen save the Earth. (wiki)