Picture is tagged "RitsuMio" and the caption under the title stays "Ricchan----!!!!!!", so I'm assuming it's Ritsu inside the costume until proven otherwise, and I tagged the picture with her name as such.
I know is Ritsu, but technically you can't "see" her in the pic. We tag what we see, and since that's not an image of "Ritsu" per se, I removed the tag.