Doppelgänger

A is an alternate version of oneself that exists in Adolla. For every person in the world, a doppelgänger exists, even for deceased individuals. Spontaneous Human Combustion is caused by their existence intruding and merging with their human world counterpart.

Overview
Much like the realm of Adolla itself, doppelgängers are tied to the collective unconscious of mankind; the thoughts and perceptions of other people are what create a reflection of a given person. This reflection possesses the abilities and memories of the original, but their personalities can be wildly different, as the doppelgänger is based on the common idea of who a person is; if an innocent and compassionate person is widely believed by others to be violent and cruel, then their doppelgänger will have a violent and cruel personality. It is currently unclear if doppelgängers all share an established goal or if individuals have their own motives.

Doppelgängers can manifest in the human world through any of a variety of different means; the most common way is that they try to encroach themselves into the body of their human world counterpart, causing them to become an Infernal. Though, Shinra's doppelgänger appeared to possess the original's body without turning him into an Infernal while the real Shinra's consciousness was lost for three months. A doppelgänger can manifest in the body of their human counterpart, but they can also manifest as a separate entity with its own physical body, as seen when Leonard Burns was stabbed from behind by his own doppelgänger, which appeared as a Demon Infernal, while Amaterasu's doppelgänger has her own body identical to the original, but completely unaware of her otherworldly origins.

Doppelgängers can appear in random people at spontaneous times, but they can also be made to encroach on specific individuals at designated times. One such example of this is being bitten by one of the Bugs. With their connection to Adolla, the bugs bite will create a link between Adolla and the person they are biting, turning the person into an Infernal, or awakening their pyrokinetic abilities, depending on whether the person is compatible or not. Another way to summon a doppelgänger is to perform a special ritual that can pull it from Adolla. The exact process of this ritual is not clear though it does require the summoner to be in a holy location and the summoner seems to experience great pain during the process, as seen when Haumea summoned doppelgängers from Adolla and brought then into the human world.

As the world heads towards a Second Great Cataclysm, doppelgängers start to appear more human, to the point of wearing clothing and being able to talk and express themselves with ease. Even doppelgängers of people who are already dead begin to appear, born from people's memories of them. These new doppelgängers appear to possess the memories of the original and use them to their advantage.

Examples
Sumire conducted a doppelgänger experiment in order to call forth doppelgängers, which involved feeding Bugs to the sisters of St. Raffles Convent, leading to them becoming Infernals. She is able to summon the doppelgängers of the children killed in the Convent fire. Amaterasu's doppelgänger would appear in Year 180 and be named Sister Iris. While the First Pillar herself is full of fury and rage, the public's belief that she is a source of kindness and mercy shapes Iris into an inherently kind person.

In Year 194, When Konro Sagamiya encountered his doppelgänger, it was a Demon that copied his movements, which Hibana viewed as an act of killing the real body to impersonate it.

In Year 198, Haumea began summoning doppelgängers from the Adolla through a painful ritual. Leonard Burns' double manifests shortly after the battle at Fuchū Prison ends. It attacks the original and drags him back into its realm.

When Shinra and Inca experience visions of the world before the Great Cataclysm, Shinra is left barely holding to sanity. While his mind is elsewhere, his doppelgänger takes possession of him. The doppelgänger worked as a part of the Fire Force but when Iris approached him, he recognised her as another doppelgänger and attacked her, telling her to be quiet about what he is.

Trivia

 * There is an urban legend about doppelgängers: somewhere in the world, there exists someone who looks exactly like another person, and if the two were to meet, one of them will die.