tl;dr current touhou wiki guidelines for adding additional touhou-related copyright tags to posts are vague and subjective and rewriting a more clear usage for them - either in the touhou wiki or their respective copyright tags - can be used to justify edits made by tag gardeners. This includes reducing the need for the full cast of one copyright appearing to having 3 or 4 minimum of the associated characters together in a post, with or without respective playable character.
Currently, the Touhou wiki states in a short sentence before the first header that a specific Touhou copyright should not be tagged unless the post makes a direct reference to it or contains the full cast from it. I propose a slight rework of that portion of the wiki to replace the requirement for the visible full cast of one game (excluding playable chars) to needing 3 or 4 or more characters from a game (excluding playable chars), without characters from other games. This means posts like post #1382643 can keep its Ten Desires tag, and posts containing 3+ residents of Scarlet Devil Mansion together without anyone (but including Reimu, Marisa, or Satsuki), like post #3991619, qualify for tagging The Embodiment of Scarlet Devil.
"Direct reference" stated in the Touhou wiki is overshadowed by the "full cast" requirement it seems, meaning people will remove a specific game copyright tag from a post which shows a spell card from said game (a clear and direct reference to the game), or remove the tag from a post parodying the game in some way (post #4546543 is a direct (and arguably obvious) reference to the title screen of EoSD but its tag was removed). References to a game will also include a character in a pose of their official art from that game (post #4495699), or Reimu wearing an outfit from a game instead of her "usual" outfit (post #4419411). For print works like Foul Detective Satori, the copyright can be tagged if the post depicts an official_alternate_costume from the work, and album works like Dolls in Pseudo Paradise is just a basic but clear reference (post #4684620 is debatable but the monochromatic color scheme matches the official art for DiPP). As something debatable, if a post has the copyright name of a work, like in post #3865937, it should be tagged wherever it's translated or in romaji text; they're for some reason being removed from such posts.
I've shared my thoughts in topic #18961 for this, which includes a bit more information than what I've written here such as visible gameplay elements qualifying for the copyright tag. I think replacing the usage part in the Touhou wiki with a condensed summary of what I've written about this issue is fair, and won't really change mistags by people who click on the related/translated tags and forget about it. Potentially having a notice in each copyright tag's wiki stating something like "do not add this tag to a post unless the post makes a reference to said tag.
So it's been a long read, but to conclude, I don't like the "full cast" requirement for tagging, say The Embodiment of Scarlet Devil if I see a 4girls post containing Meiling, Patchouli, Sakuya, and Remilia outside the scarlet devil mansion, since if I want to search for posts containing multiple characters interacting with each other from one specific copyright, I ought to do it in one copyright tag. Also, by redefining this usage in a wiki, it can prevent edit wars or arguments where the current wiki is used as the defense.
Edit: some additional points, is that while a solo post of a character is a reference to their respective work/game, it's tag bloat which is why the initial "full cast" requirement exists, and why I proposed reducing it to 3 or 4 as the minimum. Also another thing I've noticed, is the validity of tagging the copyright when a post contains only the playable cast of a game (ie. Ten Desires for Reimu, Marisa, Sanae, and Youmu together, also qualifying for the Playable Command pool).
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