Mazinkaiser is a manga by Tatsuhiko Dan and artwork done by Kōichi Maruyama. It was published on September 8, 1998 on Super Robot Taisen F Kanketsu Hen Comic. It features an original story about the title mecha and was the first among later releases of Mazinkaiser media including manga and anime. It takes place in a reality parallel to the ending of the original Mazinger Z manga where the Great Mazinger does not exist and Dr. Hell had survived the assault the Photon Lab made on his fortress. Some of the material was later used in the Super Robot Wars novel.
Having survived the destruction of his fortress, Dr. Hell infiltrates the Photon Power Laboratory and uncovers the 'Devil Mazinger' in its lower dwellings which was sealed for how dangerous it was. Dr. Hell took control of the robot and wreaked havoc on the lab wher not even the Mazinger Z could defeat it. Koji however uncovers the hidden Mazinkaiser robot that his grandfather had secretly completed. With this new robot, Koji managed to fight Dr. Hell and the Devil Mazinger and destroy the evil robot.