This article is not part of the Kuroshitsuji universe. This article covers a subject that is part of the real world. It is, thus, not in-universe, meaning it does not constitute canon or plot material in the Kuroshitsuji series.
Monthly GFantasy (月刊Gファンタジー, Gekkan Jī Fantajī), also called Gangan Fantasy, is the monthly magazine that serializes Kuroshitsuji. It is owned by Square Enix. The magazine itself usually has over 600 pages.