Doppelgänger

A is a version of oneself that exist in Adolla. For every person of the world, a doppelgänger exists. Spontaneous Human Combustion is caused by their existence intruding and merging with their counterpart.

Overview
Sumire conducted a doppelgänger experiment in order to call forth doppelgängers, which involved feeding Bugs to the sister of St. Raffles Convent, leading to them becoming Infernals.

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

Trivia

 * There is a urban legend about doppelgängers, that says there exist in the world someone who looks exactly like a person, and if the two were to meet, either one will die.