Mazinkaiser is an updated version of Mazinger Z originally created as a way for the Mazinger franchise to compete with other super powerful robots in Super Robot Wars F Final. It later appeared as the star of an OVA series by Dynamic Productions, which spun-off a few manga. As described by Juzo, while Z can give the user the power of a god or a devil; Mazinkaiser's power can exceed a god and conquer the devil.
The OVA begins with the Mazinger Z and Great Mazinger fighting against Dr. Hell's Mechanical Beasts along with the Aphrodite A and Boss Borot. While Koji believes the Mazinger brothers can handle, the robots are soon overpowered and Koji is launched from the Mazinger Z with the Hover Pilder going off in some direction. Upon landing he uncovers the Mazinkaiser, a powerful robot secretly created by his grandfather after finishing Z. As the hologram of Juzo disappears after boasting that the Kaiser can give Koji the power to exceed a god and conquer the devil, Koji goes to cockpit but loses consciousness as it fights off the Z controlled by Baron Ashura and almost destroys the Photon Power Lab. After Tetsuya and Jun leave, Koji tries to gain complete control over the Kaiser while battling Dr. Hell.