Cardinal Caterina Sforza, Duchess of Milan, often referred as Lady Caterina, is the leader and founder of the Arcanum Cella Ex Dono Dei of the Vatican. She is the half-sister of Pope Alessandro XVIII and to Cardinal Francesco di Medici. Although part of the Vatican, an organization that is against the idea of co-existence with vampires, Caterina is willing to secretly collaborate with Methuselah Empire to bring down the Rosencreuz Orden, even if discovery of her deeds would result in her execution. Her actions have placed her in a very unstable political position ("Vixen of Milan"), as well as and put her at constant odds with Cardinal Francesco di Medici, who does not believe in diplomacy and holds no regard for the Pope.

Lady Caterina is willing to die to protect her brother Pope Alessandro XVIII, whom she loves dearly. Her main motivation in the series is revenge on the Orden.

Her increasingly manipulative nature and willingness to sacrifice people to achieve her goals are not seen in the anime, as were not her unrequited romantic feelings for Abel Nightroad or her hatred for Esther Blanchett.

LOTM: Sword of Kings AA Final - Eckidina Arc

Caterina would appear in Eckidina Arc as a false antagonist turned supporting hero. To avoid the confusion of the names between her and Katarina Couteau, she was renamed into Katherine.