Dark Arts

The Dark Arts(闇術; Anjutsu) is a technique and a form of magecraft used in both DxD: Twice Critical and Highschool DxD: Яe-birth.

Unlike a magician's witchcraft based on equations and devil's imagination magic, the Dark Arts relies on the power of the Outer Gods, creatures on seemingly endless powers from realms outside time and space itslef, and how much one has contact with them and their powers.

Summary
A different form of magecraft from magician's and devil's magic, the Dark Arts are an obscure, forbidden and dangerous magical ability that grants the user the ability to communicate and receive powers and abilities from the Outer Gods, Eldritch creatures from a realm beyond ours that are said to be older than time itself and the true masters of the Universe.

Only a few individuals were able to fully comprehend and effectively use such powers, while others would go insane or perish by the sight of the Ancient Ones. Due to it's nature, the Dark Arts are hardly being able to be taught, instead being written for the generations to come and go. Apparently, due to their rather impressible and gulliable minds, humans are the only ones capable of using the dark arts, while other races would instead be driven to insanity.

Abilities
Unlike it's counterparts, the Dark Arts do not require the use of supernatural equations of the magicians of the power of the imagination from devils or the miracles from angels, but instead a link on has with the Outer Gods and the energy from their dimension.

Once one is able to withstand the eldritch presence of such, they are able to use the nigh limitless powers of the old ones in a number of ways, such as strengthening, familiar summoning, reality warping, teleportation and a type of hex that cannot be undone by normal ways unless by dark arts themselves.Due to it's alien nature, Dark Arts are practically impossible to avoid or cure simple their type of magecraft is considered both too advanced and at the same time too alien to be understood and therefore countered. The only way to stop such power is to close the user's connection to the Old One's dimension. Users of the Dark Arts are also known to have a 'foul aura' that is said to be a powerful sense of dread, which can madden those who stand in presence of them for too long, warping their concept of reality, space and time, even losing track of their own existence.

However, the strongest ability one can achieve with the Dark Arts is to summon an Old One into their realm. Such creatures of immense strength and knowledge are known to drive whoever tries to face them insane or broken, causing even physical damage for such as seem when Takumi had one of his eyes burnt out of his skull just by looking at it. It is said that if one of the dark arts users is capable of summoning a relatively strong Old One or even one of the original ones, it'll be the end of all life and light in that realm.

Drawbacks
As expect for magecraft of such calliber, only a few are able to contact the Old Ones without going insane, and even fewer are able to use their powers to their full potential without dying or going insane during the process. Even those who grow accostumate of using the Dark Arts claim they must always stay alert and concentrate during enchantments otherwise it might go awry and either turn them into Ancient Ones themselves or be dragged to the dawn of times, the place of origins of the Old Ones which is said no-one was ever able to come back from.

Because of the alien nature of the Dark Arts, drawing power from a dimension that is not ours, Dark Art users are subjected to minor transformations and mutations into their being: in order for the body to better get accostumate and withstand their powers they start to adopt Old One-like traits, as shown by Robin's unusually large tongue and Howard's cephalopod-like eyes. The longest one stays in contact with the Old One's dimensions, the more their bodies mutate, devouring both their flesh and mental health and warping their senses and organs, as shown that Conan was only able to eat raw rat flesh and sewer water without vomiting, and Howard's unusual anatomy since some of his organs have become mini-old ones themselves.

Learning
Not much is known about how one can teach and learn about the Dark Arts, even less so about their origins. The only recorded piece of information avaliable about any of such is written on several encyclopedias and hidden books around the world in a strange language which does not coincide with any other, dead or not, some of them not even completely rescued since the first thing one usually does once a book is found is to destroy it. The only book avaliable with at least some teachings about how contact and be given power from the Old Ones is known as the Necronomicon (ネクロノミコン; Nekuronomikon), a book made out of human flesh which is said to guard most knowledge of the Dark Arts.

The current location of said book is unknown since it's banning by the Pope Gregory IX and it's sealing by 777 after Conan Devlin's supposed death, but a copy of such in latin is found in possession of Robin Prelati, the descendant of the priest and magician François Prelati.

Trivia

 * The idea of such is based on the Cthulhy Mythos by H.P. Lovecraft.
 * This is the first form of magic that is not based on mythology or religion, but instead on literature.
 * Much like youkais, Eldritch tales' main motif is the fear of the unknown, drawing another parallel in Takum's adventure in the eponymous title as a Twice Critical.
 * Conan is the only Dark Arts user who's not related to someone known by their connection with the supernatural.