Zos Kias: Taken from a "dead" cult, means something to the extent of "magic to yourself." This cult was created when a follower of Master Crowley's magick theory broke away. Most of the information and magick you will hear about in this story comes from Crowley's chaos theory with little tweaks on it. In the case of this story, it's the organization they work for.
Ordo Templi Orientis: Historically and realistically, a powerful religious sect that included Master Crowley as one of its members. Although it does derive some of its original foundation from Freemasonry, Master Crowley helped form it into the organization it is today. In the case of this story, they are the group formed by Master Crowley to regulate the gates between dimensions and the organizations/people that manage them.
Warwickshire: Master Crowley was originally from the county Warwickshire in England. The city Warwick is the biggest city in the county, hence why Zos Kias' headquarters is just outside of it. You'll notice they take trips into town every now and then.
The Structure of Zos Kias: Since Zos Kias draws from direct connections to Crowley, although it's a small organization, it's broke into two divisions. The first division, the Defense division, is where most of the magic users are placed. Their duty is to handle the fighting and basic defense for the organization. Ironically, the head of the division is none other than the non-magic user Houren. The second division is the Research division, headed by Nina. Just as the name implies, they handle the intel and behind-the-scenes investigations. Most of the people that make up the division are just normal humans, who specialize in science and technology fields. Those too young to take part in Defense (usually they must be 18 years of age, Light was an exception) temporarily assist in this division, however they train alongside their fellow magic users in Defense.
The Covenant of the Luna: The thorn in Zos Kias' side! An organization made up of humans, magic users, monsters, and more. While Zos Kias and the others in the Ordo Templi Orientis work hard to keep the peace between the dimensions, the Covenant wishes for no law to govern the gates and for chaos to ensue. Their true motives are a bit vague, but they are responsible for many horrific deeds, including turning humans into lycanthropes (like Nina's older brother).
Lunae Liberi: Formed by Master Crowley himself, his own personal troop formed mostly by vampires and other creatures of "darkness." They help out the other organizations in England and Europe, as needed. Not much is known about them.
Kola and the Main Branch: This story loosely ties into another project with my sister Himeko called "Beyond Destiny's Chains." I overlapped the two stories to fill some holes, but the premise of both was the same. The main branch of gatekeepers in our world is located in Tokyo, Japan. Lillian and Kazehiko both have personal ties with that branch, thus they are quick to help out the smaller branch when its in need. The main branch is unique in the fact that most of the beings assigned to it are not from our world initially. It is common for the bigger branches, though, to have many non-humans working as higher ranking officers in them.