Nyx

Nyx (ニックス, Nikkusu lit. Night), real name unknown, is a Dark Mage, known as the Shadow Godess (影の女神, Kage no Megami) due to her being the user of Shadow God Slayer Magic, though how she learned it and from whom is unknown.

Trivia

 * Nyx's appearance is based off of Dark Sakura Matou from Fate/Stay Night.
 * In Greek Mythology, Nyx is the Goddess of Night.