At the end of Mazinger Z, Kouji was defeated through a series of events and Mazinger Z was horribly damaged. Great Mazinger came in and saved the day(enter Great Mazinger anime)
BUT, Mazinkaiser redid all of that. Mazinger Z and Great Mazinger have been working together against Dr. Hell. Mazinger Z is captured and Kouji is nowhere to be found. He comes back with Mazinkaiser and together, with Great Mazinger, they kill Dr. Hell, once and for all. In the movie, Ankoku Daishogun(The main villain from the first half of Great Mazinger) comes to take over Earh, but Mazinkaiser literally destroys the entire army and Daishogun in about...20 minutes(it took Great Mazinger about 50 episodes)
Mazinkaiser surpasses God or Devil.