Dominique de Sade, often called Domi, is a vampire of the Crimson Moon belonging to the powerful House de Sade. Born the youngest child, she grew up believing her brother Louis was a year older, unaware they were actually twins. The stigma surrounding twin births in vampire society led their parents to arbitrarily designate Dominique for survival and Louis for death. Their grandfather intervened, rescuing Louis and raising him secretly in Averoigne. Dominique resided in Altus Paris with her biological parents but visited Louis monthly, forging a deep bond with him and later with Noé Archiviste, an orphan their grandfather adopted. Their childhood involved playful interactions with village children and shared adventures, tragically ending when an attempt to save their curse-bearer friend Mina resulted in Louis's corruption and decapitation.

After Louis's death, Dominique delivered a box he entrusted to her to Noé; the wooden stakes inside deeply traumatized Noé. During his recovery, Dominique learned the truth about her twin status from her sister Veronica, who exposed their family's contempt for Louis. In a moment of delirium, Noé mistook Dominique for Louis, cementing her belief that everyone, including Noé, would have preferred Louis alive. This ignited a profound inferiority complex, driving her to adopt a masculine persona. She cut her hair short and meticulously mimicked Louis's speech patterns and clothing style. Her formerly feminine presentation shifted to tailored coats, pants, boots, and a sword sheath, reflecting her internal struggle with identity and guilt.

Dominique projects a confident, flirtatious exterior, often acting protectively toward those she cares about, especially Noé and later Jeanne. She once claimed to be Noé's fiancée as a ruse, displaying boldness in social settings. However, this assertiveness masks deep-seated insecurities and self-loathing rooted in survivor's guilt. She constantly questions her worth, convinced her family sees her as a failure and that Noé would be happier if Louis survived. Her internal monologues reveal persistent self-degradation, and she harbors jealousy toward Jeanne, whom she perceives as more capable of protecting Noé. This jealousy culminated in a suicide attempt at an amusement park, where she rationalized her death as beneficial for Noé. Jeanne intervened, saving her life, though Dominique reacted with initial hostility, reflecting her internal conflict and envy.

Her relationship with Noé remains central to her motivations. She exhibits unwavering protectiveness, distrusting Vanitas due to his influence over Noé and threatening him when perceiving a threat. Despite romantic feelings for Noé, she struggles to express them genuinely, often masking vulnerability with bravado. Her interactions with Jeanne evolve from jealousy to a complex alliance, seen when she advises Jeanne on relationships and later fights alongside her. This dynamic highlights Dominique's capacity for growth, moving from self-destructive tendencies toward tentative solidarity.

Serving as a vampire knight for Carbunculus Castle, Dominique possesses standard vampiric physical enhancements—strength, speed, and endurance—augmented by specialized combat training. Her primary weapon is a rapier, wielded with precision to subdue or kill opponents. She also demonstrates proficiency in knife throwing. Her lineage grants the de Sade family's signature cryokinesis, enabling her to create and manipulate ice by rewriting the World Formula. Unlike her siblings, who employ this power destructively, Dominique uses it with restraint, often for defense or containment. Her ice constructs can withstand immense force, such as supporting a collapsing ferris wheel, showcasing both power and control.