Infernal

The, also known as the , are victims of Spontaneous Human Combustion. Originally humans, the phenomenon causes their bodies to spontaneously ignite, and transform them into a fiery charcoal-like beings that only know destruction. The process of transforming into an Infernal appears to be quite painful and is the most feared cause of death. Infernals are considered to be a dangerous threat to human life and the world, in which the Special Fire Force have been tasked with extinguishing their bodies and purifying their souls.

Overview
Infernals 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. Infernals have no reason and rampage until their lives flicker out, which can take centuries as they do not age. 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. Infernals have also shown the ability to absorb and redirect the flames around them. The only known way to kill an Infernal is to impale their core, located in their chest, which is a painless method of returning them to the raging flames. Humans in the Tokyo Empire typically pray for the souls of the defeated Infernals, as a way of purification. As the citizens of Asakusa and China do not follow this practice, showing that the pray is not a universal custom.

Normal Infernal
This type of Infernal has dark, charcoal skin and is perpetually on fire, although their appearance differs. While typically mindless, an Infernal's behaviour can be influenced by any strong desires or personal connections they had as a human. Meaning that they may remain in a certain area. While powerful and dangerous, they can be restrained by a physically strong human for a short time.

Sentient Infernal
It is known that if a person transforms into an Infernal while having a strong attachment to life or great willpower, they will keep their self-awareness, however the level of consciousness differs between individuals. These Infernals have control over their flames and can discharge them at will, while also being fully capable of speech. It is unclear if they suffer any pain after the initial transformation is over.

Artificial Infernal
Artificial Infernals are humans that were turned into Infernals via unnatural means. Unlike regular Infernals, the heads of the Infernal are the only thing to ignite. After conducting research on Artificial Infernals and natural ones, Hibana discovered that the difference between them was that the artificial Infernals' core (upper body) had been eaten through by the Bug and left some of its biological residue and DNA inside the body. It is believe that the Infernals of immense size with multiple cores are also artificial.

Giant Infernal
A is the result of Necro Pyro being used on corpses to merge with an Infernal. Depending on if the Infernal used for the base is built for fighting, determines the strength of the colossal Infernal.

Demon
A Demon (鬼, Oni) is a more powerful type of Infernal, characterised by their more durable bodies, more powerful offence, and its ability to only be extinguished by extremely strong attacks.

Trivia

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