Dominique de Sade, often called Domi by those close to her, is a vampire of the Crimson Moon and a member of the powerful and noble House de Sade. As the youngest child of the family, her early life was marked by a hidden tragedy; she was born a twin alongside her brother Louis, a fact kept secret because the birth of twins is considered a disgrace and a bad omen in vampire society. While she was designated to live with her biological parents in the aristocratic environs of Altus Paris, Louis was arbitrarily marked for death. Their grandfather intervened, however, rescuing Louis and raising him in secret in the rural village of Averoigne. Dominique visited her brother monthly, fostering a deep bond with him and later with Noé Archiviste, an orphan whom their grandfather adopted as his student.

Dominique's personality is a complex facade built upon a foundation of profound guilt and insecurity. To most people, she projects a confident, flirtatious, and sometimes brash exterior, often presenting herself with a bold and authoritative demeanor. She speaks with an elegant yet firm tone and is known for her striking, dignified presence. This confident persona, however, masks deep-seated self-loathing and a crippling inferiority complex. The root of this internal conflict lies in the death of her brother Louis. After a failed attempt to save a curse-bearer friend, Louis's own True Name was corrupted, leading to his death by decapitation. In the aftermath, while a feverish and delirious Noé mistook Dominique for Louis, expressing happiness at seeing him, she became convinced that everyone, including Noé, would have preferred Louis to have survived in her place. This event shattered her sense of self. To cope, she cut her long hair, abandoned her previously feminine style of dresses, and began meticulously mimicking Louis's speech patterns, clothing, and mannerisms in an attempt to become the brother she believed should have lived.

Her motivations are overwhelmingly driven by her relationships, primarily her love for Noé. As his self-appointed protector, she is fiercely loyal and possessive, going so far as to publicly declare herself his fiancée, though Noé himself denies this. This protectiveness makes her deeply suspicious and hostile toward Vanitas, whom she views as a dangerous and corrupting influence on Noé. Beneath her overprotective actions lies a deep, unrequited romantic love for Noé that has persisted since their childhood. She struggles to express these true feelings directly, often masking her vulnerability behind acts of bravado or frustration, such as when she offers him her blood. Her role in the story is that of a major supporting character and a steadfast ally, whose personal turmoil frequently intersects with the main narrative, particularly regarding the history she shares with Noé and the emotional fallout from her past.

Dominique's key relationships are complex and define her character arc. Her bond with Noé Archiviste is the most central. They are childhood friends, but while she harbors deep romantic feelings for him, he views her as a cherished friend, a disconnect that fuels much of her inner pain and jealousy. With Louis, her deceased twin, she shares a tragic bond of survivor's guilt. Her desperate attempt to emulate him after his death highlights her struggle with identity and her belief that she is a living replacement. Her relationship with the curse-bearer Jeanne is particularly nuanced. Initially, she feels intense jealousy toward Jeanne, believing Noé has romantic feelings for the other woman. This jealousy is so consuming that it leads Dominique to a moment of profound despair and a suicide attempt. However, Jeanne saves her life, and in the aftermath, Dominique confesses her own affection for Jeanne, revealing a capacity for deep emotional connection beyond her rivalry. This moment marks a turning point, showcasing her potential for growth from self-destructive isolation toward tentative solidarity. Her dynamic with her elder sister, Veronica, is one of fear and intimidation, as Veronica is aware of the family's dark secrets and does not hesitate to mock Dominique as a failure.

Throughout the narrative, Dominique demonstrates significant character development. She begins as a person shattered by guilt, hiding behind a false persona and teetering on the edge of self-destruction. Her suicide attempt and subsequent confrontation with Jeanne force her to acknowledge her own worth and desires separate from her brother's memory. While she carries the scars of her past, she learns to move forward, as seen when she eventually returns to a more feminine appearance, indicating a reconciliation with her own identity. Her evolution is ongoing, moving from a place of performative bravado to a more genuine, though still guarded, strength.

As a vampire knight serving Carbunculus Castle, Dominique possesses formidable abilities. Beyond the standard vampiric enhancements of superhuman strength, speed, and endurance, she is a highly trained combatant. Her primary weapon is a rapier, which she wields with precision and skill, and she is also proficient in knife throwing. Her family's signature ability is the power of cryokinesis, the generation and manipulation of ice, achieved by rewriting the World Formula. Unlike her older siblings who use this power with destructive force, Dominique tends to employ hers with restraint and control, often using her ice constructs for defensive purposes or to contain opponents. Her ice has been shown to be exceptionally durable, capable of withstanding immense pressures, such as supporting a collapsing ferris wheel, demonstrating her significant power and precise control.