Niang-Niang

Niang-Niang is a "bizarre magician", a Magic God, who dwells in a territory beyond a certain layer of the world. Not much is known about Niang-Niang, but the being is apparently playful in nature, with his or her often ending with a star character (☆) to indicate this.

[Spoiler] After High Priest's death at the hands of Kihara Noukan, Niang-Niang intended to wipe out Academy City in order to destroy him. Before she could do so, she was 'exiled' by Kamisato Kakeru's World Rejector. [/Spoiler]

(Source: Toaru Majutsu no Index Wikia)