Gisho Getter Robo Darkness 1-4

Eight years prior to the story, explosions caused by scientists at the foot of Mt. Asama which caused a meltdown of Getter Ray energy that spread throughout all of Japan. People throughout the world began to experience some extreme mutations from the irradiation of Getter Energy that caused them to fuse with machinery and organic material and were dubbed the Idea. To combat them the Getter Robo is created by the organization GETTER and three pilots: Ryo, Hayato, and Musashi are recruited to pilot it and battle the Idea.