The mother of Takeshi Nanase and Gekkou Nanase. She treats Takeshi coldy after the incident that involved both her sons. It is revealed later that she was one of the legendary 15 magicians from the war 16 years ago and was the original wielder of Twilight. She lost her magic due to a certain incident and her connection to the Ghost Trailer's leader.
Her real name was Youko Chigi and she was the teacher of Momoka Shijou, Kippei Washizu & Kazuma Ryuusenji
She trains Takeshi in episode 10 and 11 and she seems to know something about the accident Takeshi doesn't. It was later revealed that she requested Gekkou to be killed in the 'accident' which failed in the end.The reason was that she saw Gekkou turning into Kazuma numorous times in her dreams so she tries to prevent it by requesting Gekkou to be killed in the 'accident' which failed.
Gekkou tried to kill her so she can tell him the reason why she tried to kill him then after the fight that Gekkou and Takeshi had, Kazuma saves her life.