So... is Kekkaishi finished or not?
NO, it is not finished.
Why?
The anime finished before the manga:
Anime finished: February 05, 2008
Manga finished: April 06, 2011
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
Kekkaishi is about Yoshimura Sumimura, a young man destined to protect his school from evil spirits called Ayakashi. These creatures are drawn to the powerful energy of the land where his high school is located.
Yoshimura is a Kekkaishi, meaning he has special abilities to trap and destroy these Ayakashi. He's joined by his childhood friend, Tokine Yukimura, who is also a skilled Kekkaishi from a rival family.
Together, they must work together to defend their school and town from increasingly frequent and dangerous Ayakashi attacks. They must also deal with a mysterious organization that seems to be manipulating events from the shadows, waiting for the perfect opportunity to strike.