Mage's Association

An organization created to protect those who seek to learn magecraft, regardless of nationality or field of study. (On paper, anyway.)
Their mission is the management, concealment, and advancement of magecraft.
In order to protect themselves from that which would threaten them (be it the Church, rival organizations of magi, or the monstrosities that punish humans who break taboos), they accumulated military might.
In order to further the advancement (degeneration) of magecraft, they built research facilities.
And, in order to deter crimes committed with magecraft, they created laws.
Their headquarters is located in London, and goes by the unofficial name of “The Clock Tower.”
It seems that in the beginning the Association was divided into three great branches, including the original associations that predate the Clock Tower. That is, the “Giant's Pit” of Egypt, and a cluster of associations based in northern Europe called the “Sea of Estray.” However, ever since the Clock Tower became the headquarters, mingling between the branches has been on the decline.
Also, they are fundamentally incompatible with the magecraft foundation of the Middle East and the ideological magecraft of mainland China, and the three groups are currently feigning nonaggression.

Fate/side material: Fate Encyclopedia
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A self-defense organization formed by practitioners of magegraft, transcending nationality and genre. (Of course, this is in name only.)
Its mission is to manage, conceal, and develop magecraft.
It reserves the use of force to protect itself from entities that threaten its existence (the Church, other mage organizations, and individuals who hunt what they consider taboo). In order to promote the development (or regression?) of magecraft, the Association set up research institutions and established laws that forbid the criminal use of magecraft.
The headquarter of the Association is in London, England. It is also called the Clock Tower.
The Association is divided into three departments. Besides the Clock Tower, there are also the “Giant's Pit” in the Atlas mountains in Egypt, and the “Sea of Astray,” the integrated association in Northern Europe. The “Sea of Astray” was the original Association that predated the Clock Tower, and had ceased communication with the Association since the Clock Tower became the headquarter.
Also, the Association deems the Magic Foundation of the Middle East and the philosophies of magecraft from the continent as incompatible with its teachings. Conversely, the other two schools also reject the Association.
Furthermore, as Alba stated in the story, the mage organizations in Japan did not join the Association.

Garden of sinners Pamphlet: Kara no Kyoukai Settings Glossary
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An organization created to protect those who seek to learn magecraft, regardless of nationality or field of study. (On paper, anyway.)
Their mission is the management, concealment, and advancement of magecraft.
In order to protect themselves from that which would threaten them (be it the Church, rival organizations of magi, or the monstrosities that punish humans who break taboos), they accumulated military might.
In order to further the advancement (degeneration) of magecraft, they built research facilities.
And, in order to deter crimes committed with magecraft, they created laws.
Their headquarters is located in London, and goes by the unofficial name of “The Clock Tower.”
It seems that in the beginning the Association was divided into three great branches, including the original associations that predate the Clock Tower. That is, the “Giant's Pit” of Egypt, and a cluster of associations based in northern Europe called the “Sea of Estray.” However, ever since the Clock Tower became the headquarters, mingling between the branches has been on the decline.
Also, they are fundamentally incompatible with the magecraft foundation of the Middle East and the ideological magecraft of mainland China, and the three groups are currently feigning nonaggression.
Sion is a member of the Giant's Pit, also known as the Atlas Institute.

Tsukihime Dokuhon Plus Period: Tsukihime Dictionary Revised
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An organization created to protect those who seek to learn magecraft, regardless of nationality or field of study. (On paper, anyway.)
Their mission is the management, concealment, and advancement of magecraft.
In order to protect themselves from that which would threaten them (be it the Church, rival organizations of magi, or the monstrosities that punish humans who break taboos), they accumulated military might.
In order to further the advancement (degeneration) of magecraft, they built research facilities.
And, in order to deter crimes committed with magecraft, they created laws.
Their headquarters is located in London, and goes by the unofficial name of “The Clock Tower.”

MB Act Cadenza PS2 Manual: Tsukihime Dictionary
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A self-preservation agency formed by practitioners of magecraft, regardless of nationality or race (of course, in name only).
Its directive was to control, conceal, and further develop magecraft.
The Association had the martial power to protect itself from those who threaten its existence. It also possessed facilities for the further development of magecraft. The Association enforced a set of laws that prevented the criminal use of magecraft.
At the moment, the center of the Association resided in London.

Character Material: Prelude Explanation