Demon

Demons (悪魔) are a type of supernatural being, often with considerable power and influence, found in many of the world's religions, mythologies and folklore, and connected to certain forms of Magic.

Etymology
The term demon is derived from the Ancient Greek word daimōn (δαίμων), anglicized as daemon or daimon, referring a spirit or divine power, similar to the Latin genius or numen. This initial term didn't hold the negative connotations which were ascribed to the following Koine Greek term daimónion (δαιμόνιον) with the rise of Christianity, and later any cognate words sharing the root, including demon. The anglicizations daemon and daimon are sometimes used to distinguish the original classical Greek concept from the later Christian interpretation of demons and its negative connotations.

The Japanese term akuma (悪魔) is often used to refer to demons and devils. Alternative terms include ma (魔) (often used as a suffix), maō (魔王), oni (鬼) and akuryo (悪霊) among others. Transliterations of demon (デーモン) and devil (デビル) are occasionally used.

Principles
Demons are a type of entity present in various religions, mythologies and folklore across the world. Their exact nature varies depending on the context, but they are usually described as spiritual entities possessing supernatural power and influence.

There are plenty of stories and beliefs which involve demons. Among these are various tales involving magicians contracting demons and commanding them to do their bidding, and people who make a deal with demons in order to obtain something, often in exchange for their soul. There are also various stories which involve demons individuals, much like ghosts. Other stories describe means to protect oneself against demons or how to them.

Religion, Mythology and Magic
Many religions and mythologies around the world have their own collections of demons, together with associated tales, attributes, rules, hierarchies, superstitions and other aspects. Some have demons as enemies of the gods while others have them as agents, though they are often below them.

With the rise, spread, change and decline of various religions around the world, various gods and demons from one religion, or traits associated with them, are often assimilated into other religions. In some cases, the gods of one religion may be reclassified and reduced to demons or fairies in another one that opposes it or has overcome it.

As there are many tales and beliefs which involve demons, there are also many forms of magic which use them as a basis.

Christianity
Within Christianity, the term demon is often used to refer to a fallen angel (堕天使), a concept that is typically synonymous with a wicked or rebellious angel. Demons are also associated with and most often confined to the realm known as Hell. The term devil is also used to refer to demons as conceived by Christianity.

Angels are meant to be God's perfect tools and messengers to humanity, and have no free will of their own, being described as something like remote-controlled cars of God. However they might not be able to receive commands due to failure, receive wrong commands, or malfunction, and subsequently stray from God's will, at which point they become fallen angels and have the term demon (悪霊) associated with them.

The most famous example is Lucifer the Light-Bringer, also commonly referred to as The Devil and Satan, a mighty angel who was said to be the closest being to God and once sat at the Right Side of God, but malfunctioned and rebelled, turning a third of the angels and causing a war in Heaven, before being cast down to Hell by Archangel Michael. Another example is that of the Grigori, a group of fallen angels who gave knowledge to humans on how God created Man from clay before the time of Noah. The information wasn't conveyed correctly as the humans couldn't understand the angelic language and could only create puppets of mud, golems.

Similar to angels, these demons are energy masses present in different Phases.

Though the practice of religions assimilating or reducing the deities and entities of other religions is not exclusive to Christianity, it has the most notable track record among the world's religions, being the one which brought the term demon to its current and commonly associated form. With the rise and spread of Christianity, pagan gods of old were reduced to the role of fairies or demons. This has given rise to the term to describe the process.

Christianity has various tales which involve demons and many form the basis for magic. A notable example is a widespread anti-flight spell, derived from the tale of St. Peter who when confronting the flying magician, said "Oh, demons carrying this magic user, promptly let go!!", causing Simon to lose the ability to fly and fall to his death. The Russian Orthodox Church's Annihilatus targets demons, among other supernatural entities and phenomena, for elimination.

Other
There are various methods for magicians to summon demons and bind them to a contract, compelling them to follow command(s) giving to them, even after the death of their contractor. After a summoning or contract has been completed, a summoned demon won't necessarily disappear on its own, only leaving once the spell user or another exorcises them. Aside from summoning, there are various magical techniques and spiritual items which are designed to bind or exorcise demons.

Parchment is described as being a means used to converse with demons, during a partial explanation of William Wynn Westcott's quasi-immortality, maintained by using the attraction of a great being to distortion the circulation of his life force.

A number of grimoires contain information with regards to demons and their summoning. One of the most notable is the, the first part of the Lesser Key of Solomon or Lemegeton, which contains information and instructions pertaining to the 78 demons summoned by King Solomon. Magic and entities connected to are often collectively referred to by the term.

In Kabbalah, the opposite tree to the Sephiroth, the Qliphoth, has a demon's name engraved in each of its spheres or qliphah.

One notable demon, not bound within the Qliphoth, is Coronzon, the demon who appeared to Aleister Crowley in Egypt. As well as possessing the ability to possess objects and people, Coronzon displayed the ability to animate it's host's hair and manifest a giant, sinister demonic face from it, following the old witch tradition that the devil resides in women's hair.

Background
Around the time of the Golden Dawn's downfall, the demon Coronzon was summoned by Samuel Liddell MacGregor Mathers and given one command; to pretend to have been summoned by Aleister Crowley and then guide him to ruin. Coronzon subsequently appeared during Aleister's attempt to cross the abyss and move between sephira in Egypt. After failing to hijack Aleister's body, Coronzon subsequently hid within a mountain of papyrus and travelled from northern Africa to England. Bound to follow the contract even after Mathers was killed, Coronzon plotted Aleister's ruin and manipulated events while secretly possessing the body of Aleister's second daughter Lola and acting as the Archbishop of Necessarius.

Aleister Crowley Arc
Following his defeat against Kamijou Touma, Coronzon revealed itself to Aleister and attacked him to fulfill it's contract with Mathers. After seemingly finishing him off and taking his body as a new vessel, Coronzon believed itself to have cut its ties to Mathers and was free to act as it wished, but soon learned that Aleister had diffused into over a billion of his potential selves which he had previously gathered within his body.

Toaru Kagaku no Accelerator
When Estelle Rosenthal activated the Taowu in an attempt to resurrect her recently-deceased friend Hishigata Hirumi, the Taowu and the soul of Isaac Rosenthal within it was contacted by a self-proclaimed demon, who informed them of a way to shift their soul to Keter using memories of death and achieve the Rosenthal Family's desire.

Trivia

 * Aside from supernatural entities, the term 'demon' is also used to refer to fearsome, remarkable or diabolical individuals, or flaws in a person's character or heart.
 * The term 'demon king' (魔王) is occasionally used in reference to the greatest enemy or opponent to be faced.
 * It has been noted that Kamijou Touma, when written differently, has a spelling that carries the meaning 'the One who Purifies God and Slays Demons'.