Cthulhu Mythos

The Cthulhu Mythos (クトゥルフ神話) is the name given to the fictional universe, featured in the world of Toaru Majutsu no Index, in which the stories of H.P. Lovecraft (referred to as the "genius author" in the narrative) and other authors after his death are based. It has been used as a base for spells created by certain magicians who desired to see the world described in those stories.

Principles
Since the Cthulhu Mythos is a fictional universe, spells involving it are defined as creating something from nothing.

Many stories in the Cthulhu Mythos describe the rampages of evil gods (such as Cthulhu, Yog-Sothoth and Nyarlathotep) from the perspective of humans on the sidelines - in a sense, they are a catalogue of those evil gods. These evil gods are beings no human can handle, however they all have a point in common - they all gain their role and terror from the story they represent. Ceremonies and spells using these evil gods cannot ignore this story aspect and no matter how frightening, they cannot do anything once the story has come to an end, until the next story begins.

One prominent symbol of the Cthulhu Mythos, used in certain spells derived from it, is human flesh and blood.

Background
At an unknown point after the first stories of the Cthulhu Mythos were published, magicians calculated how to recreate the despair-inducing events in them and created spells with that purpose. They compiled such spells in the Necronomicon, which was then released into the world.

A number of incidents relating the Cthulhu Mythos are reported to have occurred. These include a man attempting to use a jewel in a box to call in someone not of this world, a marriage scam artist sending someone a yellow medallion to have them meet an evil god and steal their inheritance and an old man trying to create an existence guarding a gate that would allow him to travel to another world.

One notable event occurred in the Pacific, three years prior to the current year on August 2nd, orchestrated by the magic cabal Dusk Waiting to Awaken. A ceremony attempting to summon R'lyeh caused 103 workers aboard the resource extraction ship Condor to go insane. However the ceremony, which would have wiped out the residents of every island within 1000 km had it succeeded, ultimately failed. The incident was initially thought to be sabotage aimed at causing diplomatic tension between England and America as well as the international competition over underwater resources. However after the discovery of magical symbols on the ship, England covered up the incident as being caused by rough weather and no land in sight pushing the sailors to their psychological limits, and installed a facility in the area, supposedly to calm the minds of those at sea but actually to keep an eye on where the ceremony took place.

Necessarius Special Admission Test SS
Spells derived from the Cthulhu Mythos are the focus of the events that occur during the Amakusa's admission test for Necessarius. Magicians from Dusk Waiting to Awaken impersonate them in order to steal the Necronomicon.

Using the stolen Necronomicon and a barge in the Strait of Dover, the cabal's leader Arlands Darkstreet begins a ritual to summon R'lyeh. Though this is thwarted by the Amakusa, he succeeds in obtaining data which is transmitted to another group stationed at Stonehenge, who attempt to create the new spell Blank Paper. The leader of the Stonehenge group, Vase, then utilises Cthulhu Mythos-based magic while trying to fight off the Amakusa, before they were all suddenly dispatched by a surprise attack by Freadia Strikers.

Other references to H. P. Lovecraft

 * Azathoth
 * Dagon
 * Necronomicon
 * Nyarlathotep
 * Shub-Niggurath
 * Yog-Sothoth

References to other authors

 * Hastur by Robert W. Chambers
 * Ithaqua by Algernon Blackwood and August Derleth
 * "The Moon-Lens" by Ramsey Campbell
 * Tsathoggua by Clark Ashton Smith
 * Ubbo-Sathla by Clark Ashton Smith
 * Vulthoom by Clark Ashton Smith