Mazinkaiser is a manga by Naoto Tsushima published in Super Robot Magazine on April 2002 to February 2003. It is essentially a manga version of the OVA but with a more serious tone and a few other changes. For example the Mazinger Army appear and later have upgraded forms.
The manga begins the same way as the OVA in battle against the Mechanical Beasts with Koji getting ejected from Z when he is in danger. He later discovers the Mazinkaiser and used it for subsequent battles against Dr. Hell and his Mechanical Beasts. Along the way he gains allies in the form of the Mazinger Army, but they prove to not be very effective in dealing with the Mechanical Bests. After several more fights, Dr. Hell loses his patience with Baron Ashura and has him sentenced to stasis. With the discovery of the Ghost Mechanical Beasts, Dr. Hell sets them upon the Photon Lab. As Mazinkaiser and its upgraded allies fight, the Kaiser goes to face against Dr. Hell personally. Baron Ashura had managed to escape imprisonment and allowed him/herself to be used as material for the last defense of the fortress. Dr. Hell accepts and has him/her integrated into the composite Mechanical Beast Garadoubla MK01 which fights against the Kaiser and putting it at a disadvantage until the Kaiser unleashes its full Kaiser Blade, cutting the Garadoubla in half. As Koji goes to find Dr. Hell, he finds more of the Garadoubla models that Dr. Hell explained he was going to unleash on the world. Koji shoots Dr. Hell with his Photon Gun but Dr. Hell's fallen body combines with the Mechanical Beasts to form a giant version of his head and the Garadoubla units activate. As Dr. Hell and the Garadoubla overwhelm the Kaiser, it unleashes its full power in the form of the Kaiser Nova destroying all of the surrounding enemies. While the Kaiser is badly damaged, Koji survives and gives his comrades the okay.