BEE TRAIN Production Inc. (ビィートレイン株式会社, Biītorein Kabushikigaisha?), commonly referred simply as Bee Train, is a Japanese animation studio founded by Kōichi Mashimo in 1997. Since their involvement with Noir, .hack//Sign, and Madlax (among other series) they have a strong following in the yuri fandom for being involved in series portraying strong female leads with speculatively ambiguous relationships.

Source: Wikipedia