A Flame Haze (フレイムヘイズ Fureimuheizu ) is a former human that has made a contract with a Crimson Lord to gain power. A Flame Haze's main job is to protect the balance of the world, which means destroying all Denizens that devour people to take away their Power of Existence. They are simply called as the "Hunters" (討ち手 Uchite , other meanings : seizer, vanquisher or punisher). Most Denizens cynically call them the "Tools of Destruction" (討滅の道具 Tōmetsu no Dōgu ) or "Same-race killers' Tools" (同胞殺しの道具 Dōhōgoroshi no Dōgu ). A Flame Haze normally becomes one because they wish revenge on a being that has devoured or taken something away from them. An exception to this would be Shana, who became a Flame Haze on her own volition, and had not suffered the loss of something she loved. Flame Haze generally look down upon Torches and Mystes because they are merely shells.
- Swaying Flame (炎の揺らぎ Honō no Yuragi ) - Named after the illusory scene of Crimson Realm that all human contractors caught a glimpse of while the contract is being made. This name becomes the origin of the term "Flame Haze".
- Hunter (討ち手 Uchite , other meanings : seizer, vanquisher or punisher) - The "common" term for Flame Haze. Mathilde Saint-Omer adopted this epithet and created her own title with Alastor's approval.
- Avenger (復讐者 Fukushūsha )
- Vengeful Demon (復讐鬼 Fukushūki ) - As retribution is the main cause for humans to become Flame Haze, thus this name refers to most of Flame Haze who made a contract in order to take revenge on Crimson Denizens.
- Destroyer (討滅者 Tōmetsusha , other meaning: Those who hunt and destroy)
- User of Extraordinary Powers (異能の遣い手 Inō no Tsukaite ) - The extraordinary powers refers to the Crimson Lords' unique powers given to their contractors.
- Tool of Destruction (討滅の道具 Tōmetsu no Dōgu ) - Flame Haze, like Torch and Mystes, are also viewed by Crimson Denizens as mere objects or tools for their contracted Crimson Lords to hunt them down.
- Same-race killer's Tool (同胞殺しの道具 Dōhōgoroshi no Dōgu ) - The same-race killers refer to the Crimson Lords who create Flame Haze or "tools" to hunt Denizens and protect the balance of both worlds.
A Flame Haze can be distinguished by the following details:
- Crimson Lord in Contract - A Flame Haze creates a contract with a single Crimson Lord which stays until the death of the Flame Haze or when the bond of the contract is frayed by an external event.
- Title (称号 Shōgō ) - Just like the title of a Crimson Lord or Denizen, a Flame Haze goes by a title which describes his or her ability in general. This title is unique among Crimson Lords but not among Flame Haze who underwent the contract with the same Crimson Lord. A Flame Haze usually goes by the title of "[verb] + -er/-or of [noun]" like Margery Daw's title "Chanter of Elegies" or Wilhelmina Carmel's title "Manipulator of Objects". According to the Light Novels, however, there are some mentions of Flame Haze who do not follow this rule.
- Divine Vessel (神器 Jingi ) - To contain the immense amount of Power of Existence, the contracted Crimson Lord has to stay in hibernate-like state in order to reside within the contractor's body. A Flame Haze carries a Divine Vessel which the Crimson Lord uses to watch, hear and communicate with his/her contractor. It comes in a variety of shapes and forms. If the Divine Vessel is damaged, it can be repaired given the Power of Existence.
- Color of Flame (炎の色 Honō no Iro ) - A Flame Haze shares the color of flame of the Crimson Lord he/she enters a contract with. This flame can be seen when a Flame Haze casts a Fuzetsu or Unrestricted Spells. Most Flame Haze possess a single color of flame with exceptions, like Outreniaia and Vetcherniaia (aurora-colored). Also, there are Flame Haze whose "flame" isn't flame itself, but lightning; Sophie Sawallisch is the example of this.
- Most Flame Haze are named after composers, conductors or musicians in real life; only a few Flame Haze are not in this category.