So... is Layton Mystery Tanteisha: Katri no Nazotoki File finished or not?
NO, it is not finished.
Why?
The anime finished after the manga:
Anime finished: March 31, 2019
Manga finished: December 28, 2018
... But 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
Layton Mystery Tanteisha: Katri no Nazotoki File follows Katrielle Layton as she runs a detective agency, solving bizarre and puzzling cases for her clients in London.
Alongside her assistant Noah and talking dog Sherl, Katrielle investigates mysteries ranging from cursed objects to supposed supernatural phenomena.
While helping others, Katrielle is also secretly working towards a larger goal: to find her missing father, Professor Hershel Layton, and uncover the truth behind his disappearance.
Each case she solves provides clues and leads her closer to understanding what happened to him, all while she continues to unravel the quirky mysteries that come her way.