Anna Sprengel

Anna Sprengel (アンナ＝シュプレンゲル) is a woman who was said to have helped found the Golden Dawn and supposedly carried out the role of Secret Chief, though her existence is a dubious one.

Background
In the past, Anna supposedly helped in the foundation of the Golden Dawn. She is said to have had the role of Secret Chief, and functioned as a point of contact, much like Aleister Crowley would act as a point of contact for Aiwass, described by him as one of the theories concerning the Secret Chief. However, it isn't certain whether she actually existed or whether her existence was fabricated. A letter which William Wynn Westcott supposed received from her was actually forged by him in order to give prestige to the cabal he helped found.

World War III Arc
Anna is mentioned by Aleister Crowley when he appears to attack Fiamma of the Right in Russia, despite still being in the Windowless Building. Aleister describes her supposed role and dubious existence, saying that his current state is the one that Anna was said to have had.

Aleister Crowley Arc
Anna Sprengel is mentioned by the recreated Mina Mathers during the visions of Aleister's past shown to Kamijou Touma in the Windowless Building, specifically with regards to the letter forged by Westcott.

Abilities
According to Aleister Crowley, Anna was said to have been the same higher existence that he became, existing in a different dimension, beyond just being expressible as 0 or 1, and being able to exist in multiple locations at the same time.