The idea of the series is based on the conflict between good and evil, evil represents the great Vega, an evil space commander who lives in his spaceship in outer space whose goal is to control all the planets of the universe, Vega uses in his attack on other planets robots and huge robots, and one day Vega the Great invades the peaceful planet Fled, but the Duke of Fled, the son of the king of the planet Fled, manages to escape by stealing Grendizer, who was developing on the scientifically advanced planet Fleed and leads Grendizer To outer space until he falls days later tired on planet Earth and is found by Dr. Amon, head of the Space Research Center in Japan, and adopts the Duke of Fled without revealing the truth of his personality and calls him Daisuke, the events of the series begin when Vega the Great prepares his plan to invade Earth and Vega is surprised by the presence of Grendizer on Earth.