The story revolves around Duke Fleed who is a survivor of the Vega Star, raised by Dr. Umon as his adoptive son, and known as Daisuke Umon on Earth. 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 kid sister Maria Grace), Duke decides to fight back using his best weapon, the almighty Grendizer.

Japanese Beetle helps the lonely Blue Racer make friends with humans. Beetle tries everything from making him a pet who can sing and do tricks, disguising him as a dog, and joining a hippie parade. However, all plans fail.