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Do you have permission from the publisher for an adaptation? If not, you're taking a legal risk basing it off the books.

It's based on it, it's not an adaptation.

Also, this would very well fit within fair use

That does not match my understanding of fair use at all.

It would not fit within the definition of fair use. Lack of commercial revenue isn't some escape hatch.

OTOH, if it were merely inspired by it (but not an adaptation) then there would be no copyright issues.