Nyarlathotep

Nyarlathotep (ナイアーラトテップ) is an entity appearing in stories from the Cthulhu Mythos.

In Toaru Majutsu no Index, Nyarlathotep is a being which can be brought into existence through certain spells based off the Cthulhu Mythos.

Principles
Like the other evil gods of the Cthulhu Mythos, Cthulhu is a being which no human can handle, however like them it gains it's role and terror from the story it represents. Spells which use Cthulhu cannot ignore this story aspect - as such it's terror only lasts during the 'story' and it can't do anything once that story comes to an end, until the next story begins.

As with any spell based off the Cthulhu Mythos, the summoning of Nyarlathotep is defined as creating something from nothing.

Necessarius Special Admission Test SS
Vase, a Magician of the Dusk Waiting to Awaken, makes use of a trapezohedron covered in darkness to summon Nyarlathotep while fighting against the Amakusas at Stonehenge.