Cossette is a beautiful young girl whose spirit haunts a delicate Venetian glass. With delicate eyes, long blond hair and a lithe frame, her beauty is both haunting and enchanting. She was murdered by her lover Marcello Orlando because he became too obsessed with her beauty and wanted her to stay like that forever. She convinced Eiri to enter "a pact of blood" to take revenge out on Marcello.
SpoilerIn the end she regrets dragging Eiri in to it and sends herself to slumber, waking Marcello's Cossette. Thanks to Eiri, she's reborn in Shoko.