Daiya lost everything the night a black fire erupted from the ocean. His father vanished into the sea, pulled down by a massive creature that emerged from those dark flames. A mechanical dragon swooped in to save him, but disappeared just as mysteriously. Five years pass, and Daiya has rebuilt his life as an ordinary middle schooler. Then the monsters return. The same dragon reappears, and this time Daiya understands what it really is: Daiku-Maryu, a transforming mecha whose head detaches to become Gaiking, a powerful robot built for combat. Piloting Gaiking, Daiya fights back against the creatures threatening his world. But victory reveals a terrifying truth. These attacks are just the beginning of a larger invasion orchestrated by forces from another dimension called Darius. They're coming to conquer everything. With the weight of the world on his shoulders, Daiya must leave behind his normal life and journey to Darius itself. He needs to stop the invasion at its source, armed only with his new mecha and the determination to finish what began the night he lost his father.