Brave Raideen (1975)

The demon Barao and his powerful Demon Empire awake from 12,000 years of hibernation. They were once at war with the continent of Mu, but their foes are long gone. But the people of Mu have left behind Reideen, a giant robot tasked with defending the world from the demons. The sentient robot bonds itself to Akira Hibiki, a teenage boy who is a distant descendant of the people of Mu. The robot's new pilot allies himself with Mari Sakurano, the daughter of a prominent scientist. The Demon-Mu conflict resumes in the modern era.