Bernice is introduced as the best friend of the protagonist, D'Eon de Beaumont, and a key figure in the initial stages of the story. His background is rooted in his role as an informant; he uncovers a dangerous conspiracy involving high-ranking individuals close to the French royalty. This discovery proves fatal, as Bernice is killed for the information he possessed.

Following his death, Bernice is transformed into a zombie by an alchemist, becoming an undead agent used against his former friend. In this state, he is compelled to carry out an attack on D'Eon. His primary motivation in the narrative is not driven by personal will but by his reanimated state, serving as an obstacle and a source of deep personal conflict for D'Eon. The assault by the zombified Bernice serves as a crucial turning point; during the struggle, D'Eon's blood falls upon a crucifix attached to his sword, triggering the manifestation of his sister Lia's soul to defeat the attacker.

Key relationships are defined by Bernice's bond with D'Eon, which is tragically perverted by his death and reanimation. His role in the story is that of a catalyst, whose death provides the initial lead into the conspiracy and whose subsequent attack activates the supernatural abilities central to the plot. Bernice's development is a grim one, transitioning from a living ally and source of vital information into a reanimated corpse and direct physical threat. His notable ability, if it can be called such, is his unnatural state as a zombie created through alchemical means, which forces him into a confrontation with D'Eon.