She is a Baroque Works agent. Her unique skill is to deceive people by pretending to be a nun, so that her victims can think she is harmless and this way attack them by surprise.
Kami no Gokago MetsubushiKanji: 神のご加護目潰し
Translation: God's Blinding Protection
She pulls a special cord on the cross she carries which, makes it spray a blinding smoke cloud in the opponent's face so that she can launch a sneak attack whilst the opponent is distracted.