When an evil empire called Jaaku invades Earth, a figure named Eldran, who has guarded the planet since ancient times, rises to fight it with the robot Raijin-Oh. Eldran is hurt in the battle and Raijin-Oh crashes to the ground, while Jaaku spreads its weapons, the Aku Darmer, across the globe. At Yosho Elementary School, fifth-grade class 3 is having extra lessons when Eldran hands them the Raijin Medal, asks them to protect Earth in his place, and disappears. The children go on to form the Earth Defense Agency, a mecha adventure of elementary students standing against an invading empire.