Shoko Mataki is Eiri Kurahashi's close friend and confidante. Intelligent yet plagued by deep insecurity and neurotic tendencies, she experiences intense jealousy concerning Eiri's romantic relationships, stemming from her own profound feelings for him. Her concern escalates dramatically as Eiri undergoes disturbing physical and psychological changes due to his entanglement with a supernatural entity.

Her distress over Eiri's deterioration manifests physically, culminating in a coma after she enters the antique shop linked to his supernatural ordeal. Her aunt, the local physician Hatsumi Mataki, finds no medical explanation for her condition. Shoko awakens in the final episode, coinciding with the resolution of the central supernatural conflict involving the spirit Cossette d'Auvergne. The defeat of an illusory Cossette suggests her spirit is reborn within Shoko. Upon waking, Shoko remarks that Eiri will return to paint more portraits, implying Cossette's presence or influence within her.