Square Enix has published Japanese-language guidelines for derivative fan creations. These guidelines cover Nier Replicant, Nier Gestalt, Nier: Automata, Nier Re[in]carnation, and Nier Replicant ver.1.22474487139... In short, all the Nier games!
As noted on Inside, these guidelines are broken down into several points, prohibiting things like payment for fan work, the use of Nier assets as-is (such as illustrations, plot points, in-game sounds, and music), the tracing of any art or images, and the claim that fan work is official. Other guidelines include banning the use of Nier in relation to slandering others and telling fans creators that if Square Enix asks them to pull their work, they must immediately comply.
One part, in particular, stood out to creator Yoko Taro, namely the number four guideline, which reads: “Do not harm the franchise’s image, violate public morals, or cross accepted societal norms.” The first part made sense, but the rest seemed questionable to the game designer.
On Twitter, Yoko wrote, “It appears the guidelines for Nier fan creations include, ‘Do not violate public morals or cross accepted societal norms.’ I’ve stated this publicly, but I feel like Nier itself crosses this line.”
In Japan, it is not uncommon for game and anime companies to have rules regarding fan art. It is uncommon for creators to say their own work violates said rules. Then again, Yoko Taro is hardly typical.