Diva, Saya's twin sister and the primary antagonist of the story, was born in 1833. She provides Delta67, derived from her blood, which is used to transform humans into Chiropterans. Upon birth, she was confined to an isolated tower as part of a cruel experiment. This confinement bred intense hatred towards Joel; when Saya freed her, Diva brutally murdered Joel and the attendees at his birthday party. Her isolation rendered her childish, socially inept, and oblivious to the moral consequences of her actions.
Diva rapes Riku and subsequently kills him. Following this assault, she becomes pregnant. The pregnancy prolongs her childbirth for over a year until Amshel surgically removes the cocoons from her body. In their final confrontation, Diva and Saya impale each other with swords coated in their respective blood. Saya remains unharmed because Diva's blood has lost its potency due to her pregnancy. As a result of Saya's blood, Diva begins to crystallize. Her babies emerge from their cocoons, and Diva reaches out to them, envisioning herself with her daughters and smiling at this vision before dying. It is suggested that Diva had long desired the unconditional love of a family, much like Saya's.
