In the second Mazinger-Z spinoff Grendizer, Koji is reduced to being a sidekick to the series' main hero Duke Fleed - a long stint that many Mazinger Z Japanese fans did not appreciate. For much of the early series of Grendizer, giant enemy robots are left to Duke Fleed to destroy.
In the sequel Mazinger-Z spinoff Grendizer, Koji's role is diminished to being a subordinate to the main protagonist Duke Fleed - an extended tenure that many fans of the original Mazinger Z did not find satisfactory. In the early stages of Grendizer, giant enemy robots are primarily the responsibility of Duke Fleed to eliminate.