I'm not sure who this is. It's part of a series of pictures that are all Touhou, but short black hair and red eyes are so common in Touhou that I can't figure out who this is when her costume looks nothing like any character I've seen before. No wings or ahoge, so I doubt it's Aya or Nue, no horns or streaks so it can't be Seija. Definitely doesn't look like Reimu.

I'm thinking it's randomly not Touhou after all, in which case I'm stumped.

EDIT: Thanks, henmere!