The Gunstar family has been the protector of the planet Gunstar 9 (G-9) for generations. In his youth, Dr. Brown defeated Golden Silver, a destructive android that traveled millions of miles to suck G-9 dry of all its resources. Dr. Brown was able to extract the four famous Mystical Gems, the robot's power source, and imprisoned it on one of G-9's moons.
Years later, a new menace rises. Smash Daisaku, a vicious dictator found out that the Gunstars knew the location of the Mystical Gems. One day, Smash Daisaku kidnapped the Gunstar twins' older brother Green and used a mind control machine to make Green obey his orders.
With Green's help, Smash Daisaku amassed all four Mystical Gems, has turned Gunstar 9's peaceful worker droids into deadly menaces, and is now preparing to leave for Gunstar 9's moon to reactivate Golden Silver.