lily_black
A fan nickname for a black-clad version of Touhou's Lily White, first appearing as a random encounter in Phantasmagoria of Flower View.
Doujins vary on her relationship to her canonical counterpart - some depict her as an alternate persona, and others as an entirely different character - but nevertheless she is frequently depicted as a more serious counterpart to the cheerful Lily White.
]] eventually confirmed that Lily Black is just [[Lily White dressing like Shiki Eiki. Given all the other fairies in the stage do the same, it's possible that the outfit is a uniform of sorts.