Infernal

The, also known as the , are victims of the Human Body Ignition Phenomenon. Originally humans, the phenomenon causes their bodies to spontaneously ignite, and transform them into a beings that only want to cause destruction with their flames. The process of transforming into a Flame Human appears to be quite painful and is the most feared cause of death. Flame Humans are considered to be a dangerous threat to human life and the world and because of that Special Fire Brigades have been tasked with extinguishing their bodies and purifying their souls.

Overview
Flame Humans are known to vary as individuals in terms of physical appearance, though they all form around a black figure, enveloped in flames. Some of them are more adept in combat than others and some keep their memories from the time they were humans. Flame Humans have no reason and rampage until their lives flicker out. They can launch fireballs and control the flames of their own bodies, but they also gain a noticeable increase in strength and agility after their transformation. Flame Humans have also shown the ability to absorb and redirect the flames around them. The only known way to kill a Flame Human is to impale their core, located in their chest, which is a painless method of returning them to the raging flames. Humans also tend to pray for the souls of the defeated Flame Humans, as a way of purification.

Demon Flame Human
are a type of Flame Human. Much like normal Flame Humans, they have dark, charcoal skin, but what defines them are their devil-like horns sprouting from their head. Only a select few can become Demon Flame Humans. They are much stronger than normal Flame Humans, and take a lot more power to be killed.

Sentient Flame Human
It is known that if a person transforms into a Flame Human while having a strong attachment to life or great willpower, they will keep their self-awareness, however the level of consciousness differs between individuals.

Artificial Flame Human
Artificial Flame Humans are humans that were turned into Flame Humans via unnatural means. Unlike regular Flame Humans, the heads of the Flame Human are the only thing to ignite. After conducting research on Artificial Flame Humans and natural ones, Hibana discovered that the difference between them was that the artificial Flame Humans' core (upper body) had been eaten through by the Bug and left some of its biological residue and DNA inside the body.

Victims

 * Mikako's mother fell victim to the phenomena in year 196.
 * A man boarding a train completely transformed into a Flame Human and set fire to the train carriage. He was later killed by Akitaru Ōbi.
 * Saeko fully transformed into a Flame Human, resulting in the woman damaging her husband's workplace and killing an employee. She was killed by Shinra Kusakabe.
 * Mikako's father transformed into a Flame Human while remaining partially conscious through the ordeal. He was soon killed by Arthur Boyle without any resistance.
 * Setsuo Miyamoto fully transformed into a Flame Human, murdering multiple innocent people before being captured and experiment on by the 5th Special Fire Brigade. He was killed by Arthur Boyle.
 * Masao transformed into a Flame Human and was killed by Akitaru Ōbi, with the help of Shinra, some time after the fight between the 5th and 8th Special Fire Brigades.
 * Several Flame Humans were spotted in the streets under the jurisdiction of the 1st Special Fire Brigade, one of whom was frozen by Karim Fulham.
 * Inside an abandoned building, a woman was artificially turned into a Flame Human by Rekka Hoshimiya, who immediately disposed of her afterwards.
 * Hikage's impersonator deliberately exposed himself to a Bug and was turned into a Flame Human. He was was swiftly killed by Takehisa Hinawa.
 * Haran chose to turn into a artificial Flame Human after being injured in combat, by consuming a Bug.

Trivia

 * The chant that the Special Fire Brigades preach before killing a Flame Human ("Ashes to ashes, dust to dust") is a phrase taken from the funeral service in the Book of Common Prayer.
 * Flame Humans, created by artificial means, do not appear to burn through their clothing during their transformation. It is unknown whether this is unique to artificial Flame Humans only, however, as Mikako's father was also seen wearing clothing in his Flame Human-state.