Daisuke Umon appears to be a regular person working in the ranch of Danbei Makiba, a friend of his father. However, after a visit from Koji Kabuto and later the first of an invasion by the Vegan Empire, Daisuke regains his memories as Duke Fleed, crown prince of Planet Fleed and pilot of Grendizer. With his memories restored Duke fights against the Empire with the Grendizer while tackling personal challenges from keeping secrets out of Earth's hands and the relevation of the Saucer Beasts.
Duke manages to get the Saucer Beasts on his side and reunites with his younger sister Maria Fleed. But his glee is short lived when Duke finds that his adoptive father had been uncovering artifacts from the previously ruined Mycenae Empire and found a connection to Planet Fleed. Enraged, Duke loses his patience with Earth and to keep it safe from the Vegan Empire and themselves, Duke decides to conquer Earth himself with the Grendizer. Tensions break out between parties including the Empire and the Earth's government. Sayaka finds the ancient machine Raaga and manages to escape the carnage and get the others to safety before nuclear war breaks out. Zuril, who abandoned the Empire after finding out that King Vega wanted to destroy the Earth rather than just conquer it, helps in stopping King Vega's plans by killing him. However, as the nuclear war continued Raaga's programming to wipe out humanity in case of nuclear war activates. The Grendizer gives chase, but Koji and Hikaru disengage and even when Grendizer caught up, Raaga causes a tidal wave that washes away the continents ending the nuclear war but also human civilization. Koji and Hikaru go to find survivors from the carnage while Duke, Maria, and Sayaka have entered a sort of hibernation deep beneath the Earth along with Raaga and Grendizer. Zuril had also managed to survive and decided to help bring the Earth back to life and repent for his sins.
Differences from other mediaEdit
- During the early parts of the manga, the Emperor of Darkness attempted to make a deal for an alliance with the Grendizer in order to take out the Vegan Empire. However, the alliance was short lived after the Emperor's true body is killed after his encasement was shattered.
- The Mycenae God, Raaga was revealed to serve as inspiration for the Grendizer, further establishing a connection between the Mycenae and Fleed. The same machine was used by Sayaka later in the story.
- The Saucer Beasts are revealed to be controlled by the brains of the inhabitants of Planet Fleed which were probed by the Empire. This caused Duke to lose faith in himself and refuse to fight the Saucer Beasts. Some of the Saucer Beasts even had their control broken and went to Duke's side.
- When a plan to assassinate Duke failed Blaki tried to kill Gandal, only to be killed himself.
- The events of Grendizer, Getter Robo G, Great Mazinger: Kessen! Daikaiju take place, but this chapter was just an extra as Tetsuya is still alive and he had died in Ōta's Great Mazinger manga.
- An all out war for control of Earth broke out between Duke, the Vega Empire. Duke unleashed the Grendizer's limitations and nuclear war broke out. Zuril had rebelled against King Vega and even allied with Duke's former friends. After the immense battle between Grendizer, the Vega Beasts, and Earth's nuclear missiles the planet becomes irradiated. Koji and Hikaru have managed to survive. Sayaka and the others have also survived but have been put into stasis.