The pilot movie of Grendizer. It is about Duke Fleed, a fugitive of the planet fleed, who was kicked out of his planet by the Armies of Vega. Fleed and the daughter of the king of Vega were in love before the war between their planets. The armies of Vega continue their fight with Duke Fleed.
[Source: Anime News Network]
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.
Alien invaders take over Great Mazinger who is at the entrance of a museum next to Mazinger Z as symbols of peace. Grendizer fights the evil invaders and Great Mazinger is recovered.
When the Vegan empire dispatches a new general to oversee the takeover of Earth, he quickly manages to capture Koji Kabuto and, learning of Great Mazinger through interrogation, quickly commandeers it from a museum where it was kept as a symbol of peace.
It is now up to Duke Fleed aboard Grendizer to stop humanity's former defender from becoming its destroyer.
[Source: Anime News Network]
A giant sea monster known as "Dragonsaurus" has emerged from out of nowhere, terrorizing the depths of the oceans. Great Mazinger, Grendizer and the Getter Robo G team join forces to combat the new threat. But their task becomes more complicated when Dragonsaurus swallows up Boss Borot and makes its way toward Tokyo.
[Source: Anime News Network]
Following a devastating attack by Vega's forces on planet Fleed, Duke Fleed, and Grendizer escaped to Earth. When he got there, Dr. Amon, the head of the Space Research Center, adopted him and gave him the name Daisuke. While they were working side by side in the center on a quest to find out what strange objects appeared in the city's sky! They were surprised by an attack that jolted Daisuke's memory.
[Source: official English website]