Eiri Kurahashi, a college art student working at his family's antique shop, discovers a Venetian glass among new European artifacts. Peering into it, he sees visions of Cossette d'Auvergne, an 18th-century aristocrat's daughter, reliving moments from her past. Captivated, he becomes intensely infatuated, filling sketchbooks with her image and withdrawing socially.

One night, Eiri makes direct contact. Cossette reveals her spirit is trapped within the glass, murdered by artist Marcello Orlando. Her freedom demands a man willingly bear the punishment for Marcello's sins through a blood pact. Driven by obsession and professed love, Eiri agrees.

The pact inflicts severe physical and psychological torment. Unexplained wounds appear on Eiri's body, and he endures painful visions within nightmarish landscapes. Cossette inflicts these tortures as tests of his love and commitment to absorbing the sins from her death and the curses on the household objects.

Eiri learns he is the reincarnation of Marcello Orlando, explaining his connection to Cossette and the curse. Marcello, obsessed with preserving her beauty, murdered her and her family, trapping her soul and causing grudges to seep into the glass. Despite this heritage, Eiri consciously separates himself from Marcello, vowing not to repeat the violence. He endures the pain to prove his love is genuine and self-sacrificing.

Women in his life—friend Shoko Mataki, psychic Yuu Saiga, tarot reader Michiru Yajiri, and priestess Zenshinni of Shakado—notice his deterioration and attempt interventions, including an exorcism. They fail to break the supernatural bond of the blood pact.

A critical development reveals two entities: the original spirit in the glass, who gradually develops genuine feelings for Eiri, and an illusionary Cossette born from Marcello's perfected portrait. This second entity, embodying Marcello's obsessive ideal, considers itself the true Cossette and views Eiri merely as Marcello's vessel.

In the final confrontation, Eiri recognizes the illusionary Cossette as Marcello's possessive creation and rejects it. To defeat this manifestation of obsession, he creates his own portrait of Cossette using his blood. This act of genuine love and acceptance destroys the illusion and breaks the curse.

The original Cossette's spirit departs. The narrative implies her soul finds a new existence within Shoko Mataki, who awakens from a coma displaying subtle connections to Cossette. Freed from supernatural torment and his obsessive fixation, Eiri survives, fundamentally changed. He resumes his life with indications of continuing his artistic pursuits.