Caterina Sforza, often referred to as Lady Caterina, is a central figure in the Vatican hierarchy and the commanding officer of the special operations group known as AX. She holds the powerful positions of Cardinal and the Duchess of Milan, making her one of the most influential political figures in the papal court. In her role, she is a calm and resolute leader, known for her sharp political acumen and strategic mind. She often uses a monocle, a small accessory that highlights her analytical and observant nature as she navigates the complex and dangerous politics of her world.

Motivated by a desire to protect humanity and maintain a fragile peace, Caterina is not driven by the fanatical hatred of vampires, known as Methuselah, that consumes many of her peers. Instead, she adopts a more pragmatic and diplomatic approach. Her primary motivation is to combat the terrorist threat posed by the secret society known as the Rosenkreuz Order, an enemy that seeks to destabilize the world and destroy both the Vatican and the Methuselah Empire. She founded the AX agency specifically to operate in the shadows, handling missions that are too sensitive or dangerous for the Vatican's official military forces.

Within the Vatican's power structure, Caterina's role is complex and fraught with tension. She is the sister of both Pope Alessandro XVIII and Cardinal Francesco di Medici. While she serves as a key advisor to the young and often indecisive Pope, she is constantly at odds with her brother Francesco, whose extremist views and hatred for the Methuselah put him in direct conflict with her more moderate policies. This family dynamic creates a constant political struggle for influence over the direction of the Church. Her leadership of AX provides her with a secret weapon, allowing her to act independently of her brother's authority.

Caterina's most significant relationship is with Abel Nightroad, a seemingly clumsy priest who is actually her most trusted and powerful operative. She has known Abel for over a decade and consistently entrusts him with the most dangerous and critical missions, as she is one of the few who understands his true nature as a Krusnik, a vampire who feeds on other vampires. Their relationship is built on deep trust and a shared history, and she relies on his unique abilities to counter the threats posed by the Rosenkreuz. She also commands a diverse team of operatives within AX, including the loyal and almost inhuman android Tres Iquis, for whom she is a figure of great importance.

While Caterina does not demonstrate superhuman combat abilities, her power lies in her political influence, strategic planning, and leadership. She is a master of political manipulation, using her intelligence and authority to maneuver around her rivals and achieve her goals. Throughout the story, her development is marked by an increasing willingness to take risks for the sake of peace, even arranging secret diplomatic meetings with representatives from the Methuselah Empire to find common ground against their mutual enemy, the Rosenkreuz. In moments of crisis, her composed exterior can fall away, revealing a deep, personal concern for her subordinates, most notably rushing to the side of a fallen Abel Nightroad, demonstrating that her leadership is rooted in genuine care rather than cold calculation.