The Grandmaster (盟主(グランドマスター)) is the absolute leader of Ouroboros. The body of the Grandmaster is first revealed in Sen no Kiseki IV, however most of her face is kept hidden, with her eyes barely visible. She describes herself as "a 'shadow' that declares the appointed time of the world".


The Grandmaster's first appearance was when Campanella reported the outcome of the Gospel Plan to her in the Celestial Globe. Unlike the Anguis, she laments the passing of Anguis No. 3, Georg Weissmann, during the Plan. She also laments the sacrifice of Enforcer No. II, Leonhardt, whom she had given his demon sword Kernviter through forging with Divergent Laws, and demonstrates a profound sense of responsibility over both deaths.

In S.1206, Campanella and Mariabell report to her the results of the Phantasmal Blaze Plan. She laments the many members who left Ouroboros during the completion of this plan, but reassures that it was all within her projections. She states that the lifespan of Zemuria has been extended a little due to averting the twilight, and that three years remain until the "Nothingness of All". After remarking that the Orpheus Final Plan has been going for 20 years, she announces the start of the third phase, the Eternal Regression Plan.