Grimoire NieR was a Japanese only book containing artwork, info and lore on NieR RepliCant/Gestalt. Most relevantly, it also featured stories for each of the games’ weapons — a feature that was absent from the original NieR games, but made its return from Drakengard 3 onwards.
From the comparisons shared by @dadnier, it looks like the majority of RepliCant/Gestalt weapon stories in NieR: Automata World Guide Vol. 2 are direct copies of those translated by Defade/Meru. The work of other fans used in the Grimoire NieR fan translation is also seemingly copied, with only a few minor changes made.
According to the book’s credits, the translation was handled by TransPerfect, with all fan translators remaining uncredited.
Unfortunately, this isn’t the first time a book published by Dark Horse has been caught using the work of fans. The Super Mario Bros. Encyclopedia ended up using many enemy names taken from an unofficial Mario wiki.
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