Power of Existence- It is a power that is contained within any biological or magical entity. Thus, it is not limited to reside in living humans. Crimson Denizens can steal it from humans and Torches.

Torch - It is a replacement entity for a human, whose Power of Existence is gone (dead). Torches are "shock-absorbers" for the sake of the balance in the real world. They are only temporary, and will disappear after a certain amount of time, eradicating all traces of existence related to the Torch.

Mystes - It is a special kind of Torch, who contains a Hougu.

Flame Haze - She/He is a servant whose duty is to maintain the world's balance. Each Flame Haze has contracted a Lord of Crimson Realm.

Rinne - She/He are servants for the Crimson Denizens. They vanish if they do not get Power of Existence from their master, humans, and/or Torches.

Unrestricted Methods - They are powerful magic spells, mostly used in battle in the series, but apparently usable for any purpose. They can be invoked by chanting and they consume Power of Existence. Unrestricted Methods can be seen as a blue insignia upon casting. Exactly why they're called 'Unrestricted' is unknown.

Hougu - It is the name of magical objects which can provide special abilities or even Unrestricted Methods. Reiji Maigo is a Hougu, which is able to replenish its owner's Power of Existence at midnight every day. Most Denizens, Flame Hazes, and even humans who aid them possess one or more of these.

Fuzetsu - It is a special dimension, where the Crimson Realm and the real world intermingles, and time is stopped for ordinary living beings. Flame Hazes are able to create such Fuzetsu at will, as may Crimson Denizens. However, battles in the Fuzetsu can damage real world objects, and harm the paused living beings, though thankfully for both it is possible to reverse the effects, if one uses enough Power of Existence. However, if the Fuzetsu is ever unlocked during a battle, the damage is irreparable.

Haridan - It is a crystal-like projection of the real world. It can be used to observe the location of Torches and Unrestricted Methods. From Margery's story, it is told that Haridan was made a long time ago by a Crimson Lord called The Snake of the Festival (????, Sairei no Hebi?) that had a liking to rule. He created a human city and then watched over that city using the Haridan. However, he died after having many battles with various Flame Haze. Friagne, who inherited the Haridan then brought it to Misaki city.