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Strategic-Class Magicians (戦略級魔法師) are individuals who possess Modern Magic that was created through the use of highly advanced science and technology.  All of whom wield power comparable to weapons of mass destruction. 
Only a few countries managed to develop strong military-grade magic. With the continuing practice of providing developed magic to Ally Nations, it also became normal to acknowledge Allied Magicians as Strategic-Class Magicians for their great capabilities with Strategic-Class Magic. 
It's been rumored that there exist around 50 people who possess Strategic-Class Magic.  However, only 13 people who possess Strategic-Class Magic have had their identities revealed to the world for the sake of national prestige; these individuals are known as the Thirteen Apostles.  These Magicians are seen as a big factor in the world's military balance. 
Out of all of the Thirteen Apostles, the only one who's managed to keep a modicum of secrecy about their identities is Angie Sirius —— to be precise her nickname and code-name —— not even her real face was known. 
There are rumors that a Romanian magician who goes by the code name "Dracula", is a secret Strategic-Class Magician, although the authenticity of the information is unclear.  Japan's Ooguro Ryuuya, who caused the "Great Bomb" during Scorched Halloween, is also an Unregistered Strategic-Class Magician.