So... is Hundred finished or not?
NO, it is not finished.
Why?
The anime finished before the manga:
Anime finished: June 21, 2016
Manga finished: October 15, 2018
MangaUpdates contains information about the anime adaptation and indicates that it is incomplete.
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
In a world threatened by alien creatures called "Savage," humanity's only hope lies in the "Hundred" weapon system.
Hayato Kisaragi, possessing a rare compatibility with the Hundred, is invited to attend Little Garden, a special academy designed to train users of this technology.
At Little Garden, Hayato will face rigorous training to master the Hundred and defend against the Savage.
He quickly finds himself amidst attention and various incidents as he prepares to confront the ongoing threat to the planet.