So... is Akai Koudan Zillion finished or not?
NO, it is not finished.
Why?
MangaUpdates contains information about the anime adaptation and indicates that it is incomplete.
Watching Order (by release date)
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Synopsis
In the future, the planet Maris is under attack by the Nozas, an alien race intent on wiping out humanity.
Their goal is to claim Maris as their own, using it for reproduction and expansion.
Humanity's hope rests on the shoulders of three young individuals chosen to wield a powerful and mysterious weapon system known as "Zillion".
These teens, JJ, Champ, and Apple, become the White Knights, tasked with defending their home and fighting back against the Noza invasion.
The fate of Maris and humanity lies in their ability to master the Zillion weapons and stand against the overwhelming threat of the Nozas.