BUR #31075 has been approved by @nonamethanks.
rename dark_spark -> dark_spark_(touhou)
Since 2013, the 7 times this tag has been used, 2 of them have been mistags, and I myself only ran into this tag because I was double-checking what Ultraman transformation items we had tagged on Danbooru (as one of them is called the Dark Spark). So I think it would be a good idea to disambiguate this.