Isidor is a highly skilled swordsman and heir to the Bisconti family, one of the most prestigious ducal families in the Asteia Empire. He is described as one, if not the most handsome man of his time by both women and men. He has complete confidence in himself and his abilities. According to Deborah, he does not appear in the novel she knows.

Spoiler

Isidor is the main male protagonist. Besides being a skilled swordsman, he is a great mage and also the master of Blanche, an information guild. He doesn't appear in the original work under the name of Isidore but rather under his second identity, the Master. Deborah describes him as "the crown prince's cheatkey in the novel" because he solved most of the problems in the original novel. He is, still according to her, the most capable man but also the most secret character of the unfinished novel.