A man who fell into the desert has no memory. He was picked up by Kabuto Kouji and named Daisuke. While the days seem to be peaceful, an unidentified phenomenon appears in the skies above the world's major cities. It was Vega Star, a military force from a star system far away from Earth. Humanity is overrun by Vega, which is far superior to Earth's weapons. Mazinger Z soars above the pool of water, Earth's last hope faces an uphill battle against saucer beasts. In the midst of this desperate situation, a legendary hero appears out of dust. Riding on board is Daisuke, who turns out to be Duke Fleed, the prince who was forced to flee his home, planet Fleed...

Source: Manga Productions

AniDB | ANN | MAL | TVDB | Wiki (en)

Alternative version: UFO Robo Grendizer