The series is about a 16-year-old boy Takeshi who recently formed an American football team at the Blue Sky orphanage. One day the game is interrupted by a light in the sky. Takeshi discovers he is the son of the king of the planet Apolon, spirited away to Earth by his father's retainer Labi to avoid death at the hands of General Dazaan. He turns out to have special energy abilities which can control UFO saucers from a base under the ocean floor. His friends Miki, Matsuo and Goro also become pilots. They magically change into their uniforms every time they yell U! F! O!. There are three robots: Header (Head); Trangur (Trunk) and Legger (Leg). They combine into a larger and powerful robot called Daiapolon. Through a solar-powered process known as "body fusion", activated by the "Key Energy" device placed inside the boy's chest, Takeshi can "grow" in mass and become a giant humanoid, thus "wearing" the Daiapolon as a kind of cybernetical armour.