Kubira is a demonic entity bound to Kyosuke Shigure. Her true form is a spiritual canine, though she frequently adopts a human guise—a buxom brunette with red eyes—to blend into human society. She wields shadow-based powers enabling interdimensional travel. Her existence revolves around profound devotion to Kyosuke, marked by unwavering obedience and prioritizing his safety above all else, a loyalty stemming from deep-seated personal attachment potentially rooted in love. She explicitly viewed sacrificing her life for him as her ultimate purpose.

She actively supports Kyosuke's quest for vengeance against Ohga, his sister's murderer, fighting alongside him against Ohga's forces. This includes confronting adversaries who exploited Kyosuke's grief by impersonating his deceased sister. When Kyosuke suffers critical injuries, she transports him to Isato Kaiza's residence for recovery. Later, she facilitates Shaia Hishizaki's entry to breach Ohga's defenses, though Kyosuke subsequently orders her to stay behind and tend to the injured Shaia.

Kubira fulfills her anticipated sacrifice during the final battle with Ohga. She intercepts an attack meant for Kyosuke, sustaining a fatal abdominal wound. Before dying, she expresses fulfillment, declaring dying for her master her most cherished duty. Her death occurs moments before Kyosuke delivers the killing blow to Ohga. Her actions leave a lasting impact, notably through an earring she once safeguarded; Kyosuke later gives this earring to Shaia as a significant memento.