Cossette d'Auvergne, an 18th-century French aristocrat’s daughter, meets a tragic end when her fiancé, artist Marcello Orlando, murders her in his obsession to immortalize her youthful beauty through paintings. Her spirit becomes entrapped within a Venetian glass alongside bloodstained artifacts from her murder, which absorb her family’s collective anguish, binding her soul and igniting a centuries-long vendetta against Marcello’s reincarnations.

Centuries later, she manifests before Eiri Kurahashi, a modern art student and Marcello’s latest reincarnation, demanding he atone through a blood pact of physical and psychological torment. Initially driven by retribution, her resolve wavers as genuine affection for Eiri emerges, blurring her vengeful purpose.

A second entity born from Marcello’s final portrait—an idealized depiction of Cossette granted autonomy by his obsession—claims to be her true self. This doppelgänger harbors jealousy toward the original spirit and fanatical loyalty to Marcello’s memory. Their rivalry over Eiri’s allegiance mirrors Cossette’s dual nature as both victim and embodiment of artistic fixation.

In the OVA, Cossette reluctantly accepts Eiri’s individuality, releasing her vengeance to transcend her curse. The manga diverges when Eiri’s refusal to complete a sacrificial ritual results in his accidental death, forcing Cossette to await his next reincarnation—perpetuating her cycle of longing and unresolved trauma.

Her design blends Elegant Gothic Lolita aesthetics with motifs of tragic innocence: haunting blue eyes, flowing blond hair, and symbolic interactions with candles and chains underscore her role as a spectral bridge between eras.