This character was tagged as original on the pixiv page, but she is apparently from a game or something that piromizu is doing the art for. The project site calls her "Yui", so I'm tagging her yui_(piromizu) until proven otherwise. I can't tell if it's real or a joke or whatever (since I can't read moon), but here's the site if anyone cares to clarify or whatever.

http://warasi.yu-yake.com/index.html

I can't tell if it's real or a joke or whatever

I confirmed this game by purchasing it. Tagged.