Eiri Kurahashi is a Japanese art student working at his family's antique shop. His life shifts dramatically when he discovers the image of a girl living and moving within an antique Venetian glass. This girl is Cossette d'Auvergne, the spirit of an 18th-century aristocrat's daughter murdered by the artist Marcello Orlando, leaving her trapped within the vessel. Eiri becomes intensely infatuated with Cossette and initiates contact. He learns her freedom depends on a man willingly bearing the punishment for Marcello's sins.

Eiri makes a blood pact with Cossette, agreeing to endure torment as atonement for Marcello's crimes. This pact arises because Eiri is revealed as Marcello's reincarnation, triggered by Cossette's desire for purification and release from the curse binding her and the glass objects tainted by the murder. Throughout this ordeal, Eiri exhibits self-destructive tendencies, driven by his refusal to lose Cossette and his vow not to repeat Marcello's violence against her, despite escalating suffering.

As the ordeal intensifies, Eiri confronts a second manifestation of Cossette—an entity born from Marcello's portrait, which gained its own sentience. This version, embodying Marcello's obsession, declares itself the true Cossette and demands Eiri's loyalty as Marcello's vessel. Eiri rejects this false Cossette, distinguishing himself from his past incarnation by creating his own portrait of Cossette using his blood. This act destroys Marcello's creation and breaks the curse.

The resolution sees the original Cossette's soul liberated, implied to reside within Eiri's friend Shoko Mataki. Eiri himself is freed from the supernatural torment. His journey concludes with a return to ordinary life, no longer haunted by the glass or its spirit.