Beings that traverse into the modern world from a plane of existence called the Idolosphere. They are attracted to humans with Performa; a manifestation of creative energy. Some are benevolent and aid the player-characters, while others appear as enemies and seek to drain humans of all their Performa.
The Mirages come from a world where they have engaged in endless battle, eventually losing unnecessary parts of their original self in order to become more efficient in combat. They are heroes of this world they come from. Humans that have their Performa drained by malevolent Mirages are susceptible to turning into a corrupted form of the Mirage.
The most prominent are based on characters from the Fire Emblem series, while the common encounters are derived from the traditional roster of Shin Megami Tenseidemons and Fire Emblem classes.
A Famitsu interview with members of the staff behind the game mentions that the Mirages were designed to give off a machine-like impression in order to differentiate them from the human characters and highlight the fact that they're from another world.
