As far as I have seen, the creator’s ACTUAL demands are just that they want people to properly tag their NSFW so that younger fans won’t see it.

Slap a “mature” tumblr community rating on it, or mark it E for Explicit on AO3 and bam, you are respecting the creator’s wishes.

Fancops seem to be saying that the creator doesn’t want anyone to MAKE NSFW fan work (which would NOT be a reasonable request) but I haven’t seen anyone provide proof that this is the creator’s stance.

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