Jeanne, initially called the Hellfire Witch, possesses a complex history. Her obscured origins involve fragmented memories of being discovered inside a laboratory tube filled with liquid before adoption by Louise and Éric, students of August Ruthven. She experienced a brief, happy childhood marked by energetic behavior and close friendships, particularly with Chloé d'Apchier in Gévaudan, where she unknowingly helped Chloé break her self-imposed isolation. This period ended when her adoptive parents were executed for alleged conspiracy against Ruthven's peace faction, an event Jeanne witnessed, causing severe trauma. Ruthven subsequently molded her into a Bourreau—a tool for executing vampire traitors during the human-vampire war. Wielding the crimson gauntlet Carpe Diem, she slaughtered over a thousand vampires. She hesitated when ordered to kill Chloé, resulting in Chloé's apparent suicide and Jeanne's near-execution. Ruthven intervened, placing her in a century-long slumber before assigning her as chevalier to his nephew, Luca Oriflamme, whom she protects fiercely.

Her personality reflects this traumatic past. Initially ruthless in combat yet vulnerable concerning those she protects, insults to Luca provoke extreme rage, while threats to him make her compliant, as demonstrated when Vanitas faked taking Luca hostage to subdue her. Lifelong enslavement resulted in naivety in social interactions; she struggles with concepts like class differences when Dominique de Sade flirts with her. She views relationships in extremes of love or hate, initially claiming she would rather die than pretend to like Vanitas. Deep-seated beliefs of being an unworthy "doll" manifest in self-denial of desires and fear of intimacy, fueled by guilt over her parents' and Chloé's fates. However, her relationship with Vanitas catalyzes change; his promise to kill her if she loses control to her bloodlust provides solace. She gradually embraces vulnerability, initiating intimacy despite internal conflicts about being "a pervert." She evolves into a more joyful disposition, openly expressing love for Vanitas and insisting on his inherent goodness despite others' warnings, demonstrating fierce loyalty once she believes in someone.

Her abilities are formidable. As a vampire, she possesses innate superhuman strength, speed, and endurance exceeding most of her kind, with reflexes noted as unnaturally sharp since childhood. Her primary weapon, the astermite-powered Carpe Diem, amplifies her destructive capabilities tenfold, enabling her to crush stone streets with claw swipes or unleash waves of incinerating white flames. She employs it resourcefully, such as propelling herself airborne for mobility. Though Vanitas observes her current power is "tamer" than during her Bourreau days, she remains a peerless combatant, fighting massive Beasts and armies effortlessly.

Her relationship with Vanitas progresses from antagonism to mutual dependence. Their first encounter involves violent conflict where Vanitas tricks her, forces a kiss, and declares love as a tactical maneuver. Later, he exploits her bloodlust curse—a condition restricting her from discussing its origins—by offering his blood under two conditions: she drinks only from him and uses his name. While framed as blackmail, this arrangement provides a controlled outlet for her cravings, preventing harm to Luca. Vanitas's motivations blend self-destructive tendencies and genuine concern, ensuring she feels no debt while masking his growing attachment. Jeanne initially resists but later seeks his blood voluntarily; her feelings evolve from hatred to devotion, culminating in post-battle kisses and reminders of his lethal promise. Their dynamic balances power imbalances and shared trauma, with Jeanne persistently advocating for Vanitas's hidden goodness.

Key developments include confronting her past during the Beast of Gévaudan arc. Sent to eliminate the Beast (revealed as Chloé), Jeanne grapples with guilt over her failure to kill Chloé years prior. Under Faustina's influence, she relives her trauma but is encouraged by Vanitas to voice her true desire: saving Chloé. Assisted by Jean-Jacques, she reaches Chloé, enabling Vanitas's cure. This catharsis reinforces her trust in Vanitas and solidifies her emotional shift. Later, she aids Dominique during Mikhail's interference, showcasing protective resolve beyond Luca.

Symbolism surrounds her. Her Mark of Possession resembles a rose entwined in thorns. Her April 21st birth flowers—nigella and sakura—carry meanings of secrecy, spiritual beauty, resilience, transience, and sacrifice. The sakura's association with samurai legacies and blood subtly reflects her enduring strength and acceptance of a potentially tragic fate.