Earth is invaded by the Makuu Empire, led by Don Horror, who had first destroyed a space colony near Earth. Don Horror wants to dominate the whole universe, and the Earth represents an obstacle that he has to overcome, but not necessarily destroying it. To do this, Don Horror sends spaceships to create panic on Earth. While the Makuu is trying to impose its domination, Space Sheriff Gavan from the Galactic Union Police, arrives in his spaceship, the Dolgiran. He comes from the Bird Planet, the planet where Space Sheriffs are trained and where they are stationed while on call. Gavan is asked to defend the Earth, which is his mother's planet of origin.