Dux leads the enigmatic St. Verrious-Mardious Church, also known as the Malthus Church, recruiting individuals awakened to supernatural blood-based abilities after Tokyo's Great Collapse. Her true identity, age, and past remain shrouded in mystery. She possesses long blonde hair and always conceals her eyes behind a domino mask, dressed in a gown, opera gloves, and a choker, often seen carrying an umbrella. Her speech relies on metaphors and hints, and she carefully observes others' reactions during interactions.

Pragmatic and fiercely dedicated, Dux prioritizes the church's mission above all else. She commands her followers to secure resources and allies, aiming to forge a new world even if it requires sacrificing Tokyo. Her drive stems from being an orphan taken in by the church, fueling an intense will to survive and ensure the institution's continuation through any means necessary. Though outwardly amiable, her true intentions and thoughts remain deeply concealed.