BB

BB, known as Mysterious Black Magus in the original promotional materials, is a character resembling Sakura Matou in Fate/Extra CCC.
BB is a backup AI created by Sakura containing her feelings for Hakuno Kishinami. She is said to have created the Sakura Labyrinth (サクラ迷宮, Sakura Meikyuu?), and later created both Meltlilith and Passionlip. who resemble her and Sakura.