Kasumi is the daughter of the struggling Sumadera family, and Kyrie's younger sister. Since Kyrie was the original heiress to the Sumadera family, Kasumi spent her life like a very spoiled princess. But since Kyrie cut all ties to her family when she married into the Ushiromiya family, Kasumi was forced to take up the responsibility as the Sumadera heiress. Kasumi thus blames Kyrie for all the pressures she must now face, and loathes everything about her, including her daughter Ange. She is much more open and charitable than Kyrie, though not even that can mask her malicious envy. In 1998, Kasumi participates in a feud within the Sumadera family over who will control the vast wealth Ange holds as the head of the Ushiromiya family. She also hopes killing Ange will finally alleviate some of her hatred towards the deceased Kyrie. She and her men face off against Ange on Rokkenjima towards the end of Alliance of the Golden Witch, mocking her apparent studies in magic and destroying Maria's diary, all the while being seemingly manipulated by the spirit of Eva-Beatrice. She and her men are then mysteriously killed, supposedly by the Stakes of Purgatory Ange summoned in response to Kasumi's challenge to "prove" the existence of magic.