In the future, the natural resources on Earth are depleted. People begin looking toward other planets to survive, in particular to the fictional tenth planet, Promete. Although people have hoped to peacefully settle there, a great disaster strikes as the first explorer ships are destroyed because of betrayal.
After this happens, a man named Mr. Doppler leaves toward Promete on his own ship and declares himself Chancellor of the planet. Using Promete's resources, Chancellor Doppler constructs a vast military force greater than that of Earth's. He forbids anyone from approaching the planet, under the insane belief that only he is entitled to it.
To gain control of Promete, the governments of Earth begin constructing massive combat robots. Doppler is able to attack and destroy all of them before they are completed, except for Danguard Ace. The forces sent to attack Danguard's base are destroyed thanks to the efforts of Captain Dan. Nothing is known of this mysterious man, except that he previously served Doppler while under mind control.
Ichimonji Takuma, son of the man who betrayed the initial Promete exploration team, becomes a cadet at Danguard's base. Ichimonji hopes that he might restore his father's honour by fighting against Doppler's forces.