It's not just the manga series by Mr. Pavlov. With well over a hundred images for Buront alone, and spurred on by post #573692 (depicting a scene from a recent episode on Nicovideo), I think it's probably appropriate to have a copy tag for this.
Currently one has been created (iron_of_ying&yang), but I'd suggest changing or aliasing it to the_iron_of_yin_and_yang to go with the more proper "Yin and Yang" spelling, and to avoid unnecessary use of non-alphanumeric characters in the tag.
I have no objections, but could you throw a wiki blurb at us explaining what exactly this thing is? IMHO that's much more important in adding non-mainstream copyright tags than the precise tag count.
Alright, the wiki page is done. Should I start adding the tag to images? Pretty much all of the results of a touhou final_fantasy_xi search should apply.
there are some exception. originally, first crossover between touhou and buront was "hinanawi_tenshi"+"buront".(as far as I know) they share some common features by chance(very tough body, arogant personality, magnificient sword, keywords,etc). so, they are often crossed in mugen-stories by fans. (one of the reasons which make buront be famous is he got his own appearance and voice by being mugenized)
well,sorry, anyway, what I want to say is "hinanawi_tenshi"+"buront(or his cosplay)" will also be tagged. can I remove the automatic tag later?(I think probably impossible,like elf+pointy_ears)
If it's implicated, ie. automatic, then no, you can't remove them. But this I guess was just mass-tagged, as we don't have any support for implications from multiple tags at once (that is, there's no way to say "if there's both touhou and buront, add the_iron_of_yin_and_yang automatically").