I found this image in the Mixi application "Kioku-Sketch" as Nururipon's art. (Nururipon seems to be Heus (nuntarou)'s secondary Mixi account.) Retagged.
(Subject: "Kotobuki Tsumugi")

Original URL: http://mixi.jp/run_appli.pl?id=3774&appParams=%7B%22image_id%22%3A9799461%7D