aliens, the Vegans, led by generals Blaki and Gandal, are preparing to attack Earth. Koji ignores his warnings and flies out to meet the incoming saucers, only to discover the horrible truth. In order to save Koji and protect his adoptive homeworld from destruction, Daisuke is forced to return to his true identity as Duke Fleed. He unearths Grendizer from its hiding place under the lab and sets off to fight his enemies. The Vegans establish a base on the far side of the Moon and start to attack Earth from there. Koji discovers Duke Fleed's true identity and their bitter rivalry soon turns to friendship. The daughter of Danbei Makiba, Hikaru, also discovers Daisuke's secret and becomes a pilot in order to assist him despite his objections. Later on, it is revealed that there were two more survivors from planet Fleed: Duke's younger sister Maria Grace Fleed and a man who had rescued her and fled to Earth, raising her under the guise of her grandfather. Caught in a crossfire between Grendizer and a Vegan beast, he reveals to Maria that she is the last survivor of the royal family of Fleed (under the belief that Duke was killed) before dying from his wounds. Maria swears revenge on Grendizer and its pilot. She tries to ambush Duke, Koji and Hikaru at the Space Science Lab, but the fight is short. Maria's attacks bring Duke's necklace (which is the same as the one she wore) into view and the truth is revealed. The lost siblings are reunited at last and Maria becomes the last addition to the team. As the conflict nears its end, it is shown that Duke Fleed was engaged to King Vega's daughter, Princess Rubina, prior to the attack on Fleed. When Rubina discovers that planet Fleed is no longer polluted with Vegatron radiation and that her fiancé is alive and well, she rushes to Earth to bring him the good news. Unfortunately, one of King Vega's generals uses this opportunity to ambush Duke Fleed, and Rubina is killed when she takes a shot aimed at Duke. This makes Duke even more determined to wipe out the Vegan menace once and for all. King Vega decides to gather his remaining forces and make an all-out attack on Earth, destroying the Moon Base to coax his troops into fighting to the end and finally succeed in invading Earth