Orsola Aquinas (オルソラ＝アクィナス Orusora Akwinasu?) is a nun-in-training formerly under the Roman Catholic Church, who specializes in preaching to pagan countries, and in decoding written codes. This skill in decoding puts her into the harm's way as she wanted to decipher and destroy the infamous Book of the Law, prompting the very institution she is in to attack her, and forcing her to seek refuge. She is first introduced in Toaru Majutsu no Index in distress, and her plight and struggle is chronicled in the Orsola Aquinas Rescue Arc.