Necessarius

is a secret branch of the Church of England that conducts supernatural and magical experiments to fight supernatural threats. They are also referred to in Japanese as the "Church of Necessary Evil" as this organization is created by English Puritans who despise magic, but since Britain was a magical country during their time, they had to learn to use magic to counter magic, which was regarded as derogatory. Despised by Purists and forced out of Canterbury, the headquarters of the Puritans, Necessarius continued to contribute behind the scenes, building its power overtime, and ending up with Necessarius being the main power behind the Puritans. The headquarters is located at a St. George Cathedral in London. .

At first, they are allies of the Vatican and rivals with Annihilatus, the Russian Orthodox Church (ironic, as the organization's headquarters in real life is of Orthodox Denomination), but later on, Necessarius, and by extension, the Anglican Church of England, ends up in an alliance with Academy City against the Roman Catholic Church. The leader of the Necessarius is led by a seemingly young female Archbishop (who is also the Archbishop of the Anglican Church) named Laura Stuart, a person who noted by various people such as Lidvia and the Pope as someone who is truly capable.

Most of the members are former antagonists but are now changed thanks to Touma's efforts (sometimes by force).

Membership
There is no mention of any formal ceremony involved whenever a new member of added to the church's affiliates, but it is implied that there are no such rituals, as former Roman Catholic Church nuns Agnese Sanctis and her subordinates are automatically added to Necessarius's affiliates after they agreed to join, under the name of "Roman Catholic Church, United Kingdom Branch". The Amakusa Church is also affliated with Necessarius, despite not having converted to the Anglican Church.

Some female members of Necessarius prefer wearing the attire of the English Puritan Church, a tunic tied along the waist with a cloth and is sometimes worn under a scapula. They usually follow a color scheme made up of the colors white and gold. Male members have a more liberal clothing scheme as depicted by current member Stiyl Magnus. Other members which are more active in field work like Kanzaki Kaori prefer to wear clothing other than the English Puritan Church's uniform.

Individuals like Kamijou Touma and Himegami Aisa may not be official members, but they are also affliated with Necessarius.