>>282403172
Mazinkaiser's first manga appearance was actually an adaptation of the last part of the Super Robot Taisen novel (which in spite of the title was just a Mazinger/Getter novel, centered on the Mazinger cast) which featured God Mazinger, with Kaiser pretty much replacing God Mazinger as the Mazinger Z upgrade. It's actually kind of odd this wasn't adapted in favor of just doing a Mazinger Z remake for the OVAs.

The idea there was going back to the whole "you can be a devil or a god", but this time they literally had the power to do that. In the novel, Juzo's true prototype that he locked away due to fearing its consequences to the world turns out to be the "Devil Mazinger" which is eventually implanted with the brain of Dr.Hell, becoming an actual uncontrollable devil before it goes on to absorb the Mycanae Emperor and Grendizer. Then you Yumi building God Mazinger/Mazinkaiser as a rebuild Z based on Juzo's "true" plans, similar to the Devil Mazinger.

If you play SRW, it's from this where it pulls the whole context about Mazinkaser being hard to control and having modes that seal its capabilities and even the Kaiser Nova attack. With Kouji needing to liberate its power to win but also avoiding becoming controlled by it and becoming another Devil.

The original novel came around the same time as SRW F/FF and God Mazinger's original design was fairly Kaiser-like already (although the heat emitters had a very different shape), so it was all probably planned at around the same time. It's just the anime didn't go with it and just rehashed Mazinger Z, but to this day you can SRW (or even the Kaiser OVA manga adaptation) pulling from it to bigger or smaller degrees.