Omamori, also known as Omamori-sama, is a zashiki warashi, a type of household spirit traditionally believed to bring good fortune to the home it inhabits. In Ushio & Tora she appears as a small childlike spirit with dark hair and dark eyes, and her backstory is tied closely to the Takatori family. The family kept her imprisoned within a protective barrier so that her fortune-bringing nature would guarantee their continued prosperity. During that long confinement she was not entirely isolated; she was visited and comforted by a succession of white-haired women connected to the household, including the mother of the young girl Saya Takatori, and later by Saya herself, who spoke with her and offered her warmth and companionship. Because of this, Omamori developed a prophecy that a boy carrying a spear would one day come to free her from the barrier.

Her personality is gentle, patient, and quietly resilient. Although she was effectively a captive used for the family's benefit, she did not become bitter, and she maintained hope through her belief that her liberator would arrive. When Ushio came to the Takatori house and prepared to break the barrier that held her, she initially resisted because the destruction of the barrier threatened to cause a lethal backlash. She relented only after Tora intervened, and her release marked the beginning of a personal transformation. Freed from the duty imposed on her, she gained confidence and independence, a change reflected in her appearance as her hair turned brown, symbolizing her liberation from the ancestral obligation that had bound her.

Her motivations center on freedom, gratitude, and loyalty. Rather than leaving after gaining her liberty, she chose to remain close to Saya, watching over and protecting her even after the Takatori household was destroyed. She also became a supporter of Ushio during the conflict involving the yokai of Tono, siding with him and even speaking to the spirit Osa on his behalf. Through these actions she shows herself to be a steadfast ally whose loyalty is given freely rather than compelled.

Within the larger story she serves as a supporting character whose liberation is connected to Ushio's visit to the Takatori residence, and she continues to appear as a guardian presence linked to Saya. Her development moves her from a passive, confined spirit dependent on the kindness of visitors to a self-assured guardian who actively chooses whom to protect. Notably, she is able to close the Gates of Hell, a feat she performed in place of Saya Takatori, and like all zashiki warashi she brings fortune to those she watches over. These abilities, combined with her gentle nature and growing confidence, make her a quiet but meaningful presence whose loyalty and gratitude define her role in the story.