El hombre que cayó al desierto no tiene memoria, llamado Daisuke, se lleva bien con Kouji Kabuto, quien lo recogió. Después de eso, un fenómeno aéreo no identificado ataca la tierra, y la esperanza de la humanidad, Mazinger Z, es derrotada, y en medio de una crisis absoluta, aparece el robot gigante Grendizer y rechaza la fuerza no identificada. Daisuke estaba a bordo. Era Duke Freed, un príncipe del espacio que fue expulsado de su ciudad natal.

Duke defeats the Vega forces, but loses his senses and flies away eventually landing on Ogami Island. Koji follows him and just as he meets the island's shrine maiden Hikaru, his arch enemy Cassado attacks Earth.

Duke's anger burns up in the despicable cassado. He makes Grendizer run wild, but he remembers his promise to Koji and stops. Duke regrets that he got on again and cheers of gratitude.

Reunion with childhood friend Naida. It brings a brief moment of peace to Duke. However, she approached Duke as an enemy of her brother Sirius. The blade of love and hate is approaching.

Teronna, a female knight who can be said to be Duke's best friend, landed on Earth. Unlike the previous Vega army, Teronna offers a fair game, but she condemns Duke as a planet sinner.

Investigation of super-ancient ruins was underway on Aijin Island. A new weapon of the Vega army is released in the nearby sea. Grendizer is dragged into an unexpected battlefield and has a hard time. At that time, a mysterious shadow approaches.

Duke receives a message from the flying beast and reunites with Rubina, who has come down to Earth. Duke begins to tell the truth about the tragedy on Planet Fleed.