Demons (悪魔, Akuma)? are the main enemies (and possible allies), and a key feature of the Megami Tensei franchise.
In the Megami Tensei franchise, "demon" refers to any supernatural entity that can bring harm to human beings or interfere with their lives in one way or another. This includes more conventional malevolent demons, folktale creatures, deities, urban legends, and Judeo-Christian angels.
Although classified as demons, angels tend to differentiate themselves from demons, and likewise the demons view them as separate. Angels also includes demons that have submitted to God and have become His servants.
Shin Megami Tensei IV Apocalypse
"Once a term used to describe the anthropomorphized versions of natural phenomena or, in certain cultures, minions of evil. Presently used to describe the non-terrestrial life-forms that appeared after God's Plan. The term encompasses a variety of creatures across a spectrum of cultural backgrounds.
There are over fifty known demon races, identified by appearances and origin
Modern reports of demons place their emergence in the 1980s, though at the time their presence was so low that they were often dismissed as urban legend. After the incident with the Yamato Perpetual Reactor in which a gate to the Expanse was created, the demon population surged. Following God's Plan, reports of humans turning into demons also began to surface, although the cause for this remains unknown. One theory asserts that the magnetite found naturally in all humans is somehow able to react to will and desire, sometimes triggering said transformation. If true, this theory would mean that all humans are then capable of becoming demons. The bulk of this theory comes from reports about human consumption of Reds, but because evidence of Red-induced transformation into demons are so rare, the theory remains speculative at best.
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Last Bible series
Known as monsters (魔獣, Majū)? they are a race of creatures that coexist with humanity. In the first game it was the Gaia Masters who revived the extinct race, and with the exception of Mephisto sought to protect their existence.
In the Persona universe, known as Personas, gods and demons exist within the universal unconsciousness, which exists due to the Star Eater's influence. To resist the Star Eater's wave-like psyche, which was left on the surface after its main body became the moon, and stood as a contradiction to themselves, Earth's primitive life evolved a universal unconsciousness and the gods and demons within it. Gods and demons emerge from humans as a way of defending their psyches from the Star Eater.
Humans can also turn into demons if their psyche is destroyed, or if they are artificially given a different Persona after having theirs forcibly removed, especially in the cases where the extracted persona was artificially granted, as happened with Shiori Miyashiro, whose metamorphosis into the demon Wendigo was documented by Takahisa Kandori and the New World Order.
In Persona 5, demons appear in the form of humanoid Shadows who manifest within the Palaces of Shadow Selves, serving as guards and as minions. They do not initially remember being anything other than a Shadow, but can be reminded of their true origin from the Sea of Souls during negotiation. During a battle, their Shadow forms dissolve into red puddles that become their true forms. If cornered in a Hold Up or scared into surrender, they can negotiate with Phantom Thieves of Hearts for items, the return of captured party members, or to become new Personas. The Shadow Selves (and similar entities) also have demonic forms that erupt from the body, destroying it in the process.
Devil Children series
Demons are entities that reside across the countless worlds that exist in the Devil Children 'verse, created alongside humans and angels by the creator goddess Hoshigami. The power, lifespan, and whether they are part of a race of demons with the same name or an individual varies from demon to demon. A demon's soul can be found as a gem or floating spirit, allowing for the demon to be resurrected using means such as Relic Fusion. Unlike other franchises, demons are implied to not be born from the belief or emotions of humanity.
Digital Devil Saga: Avatar Tuner series
Demons are a person's true self, brought forth through the Atma virus that turns humans into avatar tuners. Some demons are able to dominate their original human personalities and take the place of their host, while others find either coexistence or an identity crisis born in others.
A staple gameplay feature of the series is the ability to negotiate with and/or recruit demons as allies and party members, usually through the use of a COMP with the Demon Summoning Program installed; many demons will request Items or Macca in exchange for their services. In some games, most summoned demons require Magnetite in order to maintain their corporeal forms; without a constant supply they will lose HP with each step.