Hades Project Zeorymer (1988)

Masato, a seemingly typical high school student, has his life turned upside-down when he is suddenly arrested without explanation, after which his parents show up and tell him they aren't his real parents, but actually, government employees paid to pose as his mother and father. He later learns that he had been selected (apparently a long time ago) to be the pilot for a giant fighting robot called the Zeorymer. His assignment is to fight Hau Dragon, the shadowy organization that built the Zeorymer, along with seven other robots they still control.