The Doron Empire, originating from the Ganymede System, identified Earth as an ideal planet for conquest. Their expansionist ambitions were sparked by the power-hungry General Ozmel, who overthrew the reigning Queen Medusa of the Ganymede System, initiating a universal campaign of domination.
Earth, nearly overwhelmed by the empire, is on the verge of collapse. One scientist, Dr. Shikishima, holds a single hope for restoring the planet from its alien invaders: a massive mecha called the Mechander Robo, specially programmed and designed to combat these extraterrestrial forces and prevent a complete takeover. Alongside this formidable fighting machine, Dr. Shikishima recruits three pilots to man the Mechander Robo's controls: the enigmatic Jimmy Orion, the scientist's son Ryosuke Shikishima, and Kojiro Hachijima.
While the main narrative revolves around Earth's struggle against the Doron Empire, there is a hidden aspect within lead pilot Jimmy Orion's past that is somehow linked to the overarching storyline.