Flame Haze is a person that has his/her existence eaten by a Crimson Lord, and in exchange the Crimson Lord will turn him/her to an immortal being with superhuman power, in order to fight one who bring danger for the world's balance.
Flame hazes are avengers. They became a flame haze in order to take revenge on a certain Guze no Tomogara that kill their important people, like their family, friend, lover, etc. But, there are exceptions like Shana and Mathilde, they became a flame haze because they want to. Shana don't have any specific revenge on Tomogara (Denizen). Their vengeance is the one that make them can survive very long. Some flame hazes die because they commit suicide, because they are tired to live. After they took revenge, usually they will retire (if they're not die) and stay on an outlaw.
Flame haze hunt Tomogara to maintain the two world's balance. According to their mission, they kill Tomogara that bring danger to the balance, and they should not hunt Tomogara that care for the balance. Still, many flame hazes deviate from the mission due to their hatred towards Tomogara, still targeting harmless Tomogara like Rammie.
Flame Haze can be killed if he/she is injured with a fierce, or the Jinki he/she carries is destroyed. Flame Haze perish if the contractor cancel the contract, of if he/she is shot by Trigger Happy (the Lord who reside inside them will be awaken and they can't hold the Lord's big existence).