The story centers primarily around the Temple and the school. This means that most characters are of high school age, or at least appear that way. Characters from other worlds must be accepted by the temple as students there if they don't assume a relatively normal human life. There are rules about blending into the human world that allows no exceptions.

Ningenkai - Humans, normal, abnormal, but basically human. Born from two human parents and living in the dull and boring world, going to school, stuff like that. Humans can have psychic powers or other gifts, but nothing too extreme.

Reikai - These are Spirit World beings. They are the ones who guide human souls as they depart earth, process them, send them on their way to (hopefully) the right place. Some of them are humans who have died and are now employed, or they can be born Reikai. They appear normally in the Ningen realm, but their spirits are much stronger and can travel from their bodies easier. They have various powers including teleporting and mental powers, based on their position.

Makai - Creatures from the demon world. They aren't necessarily bad, most of them are just trying to survive, but some of them can get really nasty. Some can live well-hidden in the human world.

Just because the words "makai" and "demon" are loosely interchangeable does not mean Makai are the Western concept of demons, they are not the same.

There are many types of Makai. There are just about as many different Makai as there are countries in the Ningenkai.

Youkai (Fire demons) - The most populous and also the "rulers" of Makai. There are dozens of clans, each with different powers and levels of status. The Dragon Clan is the ruling lineage, while the Shadow Clan are the current "bad guys"

Koorime (Ice demons) - They are very rarely found off their floating island high above Makai, but Koorime has recently been invaded by the Youkai...

Kitsune (Fox spirits) - The so popular Youko. In Makai they inhabit an entire forest that other Makai fear to enter. They keep to themselves, don't answer to the Youkai rulers, and basically love wreaking havoc. They are generally thieves, spies, or assassins by trade.

Nekojin (Cat demons) - These are totally different from feline Jujinkai. They aren't numerous in Makai anymore, and really just blend in with the Youkai, concentrate in the Makai cities, and just survive. Most have been enslaved by Youkai, so their numbers are small.

Mythicals - A creature from Japanese myth that wouldn't fall under Makai or Jujinkai. For example, werewolves aren't quite Jujin, and some types of vampires aren't quite Makai. And the Ki'lin are just... well mythical.

Jujinkai - Creatures from the man-beast world, a fairly young world in the scheme of things. This world is primitive, wild, and very anti-social when it comes to the other worlds. They live long long lives and usually have a thing against Makai. They have powers, including limited beast attributes, and they are very strong. A 500 year old Jujin with proper training can have their arm cut off and it will heal good as new very quickly. Jujin come in plenty of varieties depending on their line - feline, canine, avian - basically any beast given human attributes. Most of the population consists of the feline or canine varieties.

Half-breeds - What the name says, dad was one thing and mom was another.