The video game is based on a manga created by Go Nagai. Set in a different universe from the original Mazinger story, the story begins in the year 1999 AD, when God Kaiser Hell began an all-out invasion to control Earth using powerful giants known as 'Bio Beasts'. Mazinger Z in Mazin Saga is actually a suit of armor rather than a robot. This armor has the ability to transform into a giant version of itself, allowing Mazinger Z to battle the Bio Beasts.
Mazinger Z's design in Mazin Saga is a departure from the rest of the Mazingers. Here, Mazinger Z is given an all-blue color rather than black in white like the others. Colored orbs are mounted on Mazinger Z's crown and torso. In many instances, Mazinger Z dons a red cape and it's only weapon in combat is a sword, similar to God Mazinger.
The characters from the original Mazinger Z series reprise their roles in Mazin Saga, albeit slightly different from their anime/manga counterparts. Dr. Hell appears in Mazin Saga as God Kaiser Hell. Koji Kabuto still plays the protagonist, but has as darker, more serious persona than featured in the anime and manga versions of Mazinger Z (which is understandably so, given the setting and mood of Mazin Saga being close to another of Go Nagai's works, Devilman). Even Garada K7, one of the earliest enemies Mazinger Z fought in the original series, reappears as a Bio Beast.