When Tsuwabaki Daiya and his father are sailing in a small boat, Daiya discovers a black flame erupting from the ocean. A gigantic monster emerges from the fire, and the father and the crew vanish into the sea. Just as Daiya is about to become the next victim, a colossal mecha dragon appears and rescues him. Five years later, Daiya is a junior‑high student. A new, enormous monster surfaces, and Daiya encounters the mecha dragon known as Daiku Maryu. The dragon’s head detaches from its body, transforming the remainder into the chassis of the super‑robot Gaiking. Daiya pilots Gaiking, defeats the monster, and learns of an enemy intent on conquering the world. He then travels to the other world of Darius to thwart that plot.