So... is Kiseijuu: Sei no Kakuritsu finished or not?
YES, it is finished.
Why?
The anime finished after the manga:
Anime finished: March 26, 2015
Manga finished: December 23, 1995
MangaUpdates contains information about the anime adaptation and indicates that it is complete.
Watching Order (by release date)
Here you have all the anime relations we detected ordered by release date, so you can see the reason for this status in context and also use it as watching order.
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Synopsis
Parasitic aliens invade Earth, taking over human hosts and disguising themselves to hunt.
Shinichi Izumi, a high school student, is attacked, but the parasite only manages to infect his right hand.
This parasite, named Migi, and Shinichi are forced to coexist, working together to survive.
They must defend themselves against other, more dangerous parasites who see them as a threat to their existence.