ネロ

With a child-like appearance and known as "the greatest and most wicked magician" in the world, Nero is the only female Anticross member, with the grimoire Unaussprechlichen Kulten (無名祭祀書 Mumei Saishisho, lit. The Book of Nameless Rituals) and the Deus Machina Nameless One at her disposal. In order to deceive Kurou, Nero feigns amnesia and gains his trust by developing a second personality called Ennea (エンネア).[From Wikipedia.]