A survivor of Fleed Planet escaped from there on a special spaceship designed by Dr. Umon and reached Earth. His name is Duke Fleed and he is the adoptive son of Dr. Umon. After reaching the Earth he knew about King Vega. Who wanted to conquer the earth with his army and then Duke wanted to stop him. He and his friends Koji and Hikaru help him in this and they use a special weapon that is designed by Umon, a Grendizer. グレンダイザーU