Duke Fleed is a survivor of the Fleed Planet who is escaped to the Earth, onboard a mysterious spaceship, where is raised by Dr. Umon as his adoptive son, and known as Daisuke Umon. Years after his arrival, he's faced with the threat of King Vega and his army, who want to conquer the Earth. With his friends Koji and Hikaru (and later his younger sister Maria Grace), Duke decides to fight back using his best weapon - the almighty Grendizer.

The third season doesn`t have a particular story behind everything (like Valkyrie Ghost in the second season). It just tells 6 stories about the life of Kazuto & Co. with some additions: Raine and Chorus get a house on earth, the last three Valhalla princesses each get an episode, and in the last episode Kazuto and Valkyrie, who in the same episode managed to stay adult, >try< to marry again. (Source: ANN)

The Chojin Crown, the tournament which Mantaro (Kid Muscle) reluctantly participates in. After going along with the obstacles (most of which were created to try and eliminate him), he qualified. (Source: Wikipedia)

Unaired episodes included with the Blu-ray volumes.