Fairy

Fairy (妖精) are legendary creatures in European folklore. In the world of Toaru Majutsu no Index, legends surrounding different kind of fairies are used as a basis for magic spells.

Principles
According to Ollerus, fairies were pagan gods of old that were changed when Christianity became much more prevalent. Simply put, they shrank down the pagan gods (though without being aware of it). The king of the forest transformed into a dwarf. The queen of the sea was remade into a female monster that sank ships. One theory said the gods of the many old religions that conflicted with Christianity were reclassified as evil gods who fell under the category of demons. Those became clear enemies, but there were others that had been remade into beings that lived alongside mankind.

Fairies are apparently seen as diminutive beings, being referred to as "small neighbors". They are also seen as either malicious or enigmatic, kidnapping people and ate their insides, or helped with one’s job or housework if certain conditions were met. Despite the spread and power of major religions in forbidding belief in them, fairies have remained in people's hearts. These beings had not been completely remade as enemies or completely eliminated. Unlike the evil gods whose great power was recognized but were seen as merciless enemies, most of these had managed to remain unchanged in people’s hearts on the condition that they were made powerless or shrank down.

In the modern age, the word "fairy" has become commonplace. Religions did not treat it as taboo. And children’s fairy tales and picture books, such as, , and are well known. However, very few people had accurately extracted their true form and original role from the flood of information. It was similar to how the great mixture of information on the modern internet diluted the trustworthiness and credibility of the information found there.

Characters that use fairies and fairy tales in their magic

 * Skogsfru (Skogsfru)
 * Vasilisa ("Vasilisa the Beautiful")
 * Theodosia Electra ("The Little Match Girl")
 * Saronia A. Irivika (Leshy)
 * Cendrillon ("Cinderella")

Turn into a fairy
"…This is the end. Even if humans cannot kill a god, we can manage against a fairy."

- Ollerus to Othinus

Ollerus, a magician who failed to become a Majin or Magic God, researched fairies and fairy tales and the weaknesses of a magic god in order to stop Othinus and her nefarious plot. He made a spell based out of the historical fact on how pagan gods were turned into fairies during the rise of Christianity.

Called Turn into a fairy (妖精化), the spell is specifically created to counter Othinus the Magic God and bring her down into a field where she can be defeated. Fiamma of the Right was also tought of this spell as a back up when Ollerus' attack fails on Othinus. The spell appears as a glowing stake that comes out of the user's open palms, and is supposedly used by piercing the target's chest. The spell, if working properly, is able to thoroughly destroy the interior of the target's body.

After Ollerus fails to defeat Othinus with the spell, she immediately knows how to use and uses the spell on Ollerus. As Ollerus too has stepped into the territory of a magic god, he too is vulnerable to his own spell. However, after she is forcibly turned into a fairy by Fiamma of the Right, she still became a complete magic god, for her becoming a fairy, though meant that she could no longer become a magic god, it also freed her from the 50/50 restraint of her power as she only needed to either gain 100% success or failure. Thus her being utterly thrown down into a fairy showed that she failed to become a magic god, it inadvertently turned her back into a magic god but now a complete one.

Later on, after the destruction of Gungnir, Othinus is forced to use this spell, representing her negative possibilities, to attack Touma. This later causes her to start losing her powers as a Magic God, as originally intended.