Tadatsuru Teori is a rogue oddity specialist known as a dollmaster, focusing specifically on immortal dead oddities, contrasting his contemporary Yozuru Kagenui's expertise in living immortals. His obsession stems from viewing oddities as aesthetically beautiful creatures, leading him to capture them for personal study rather than extermination. This fixation ultimately drove him to experiment on himself, with disastrous consequences for his existence. During college, Tadatsuru belonged to an occult research group alongside Izuko Gaen, Meme Oshino, Yozuru Kagenui, and Deishuu Kaiki. Together, they created the artificial tsukumogami shikigami Yotsugi Ononoki using a human corpse. Yotsugi's choice of Kagenui as her master over Tadatsuru established a lasting rivalry between them. Their manipulation of life and death also inflicted a shared curse: Tadatsuru and Kagenui became unable to touch the ground for life, described as punishment for "not knowing their place." Leaving Gaen's network due to conflicting ideologies, Tadatsuru operated independently as a stray specialist. He later attempted to transform himself into an immortal oddity using the method that created Yotsugi, but the process failed catastrophically. His human body died and passed into the afterlife, yet he retained the ability to remotely control multiple mass-produced dolls modeled after his original form. This allowed him to interact with the living world despite his spiritual state, a secret known only to Gaen, Oshino, and eventually Koyomi Araragi. Replacing destroyed dolls was taxing, limiting his effective immortality. In Tsukimonogatari, Tadatsuru kidnapped Suruga Kanbaru and the Araragi sisters, Karen and Tsukihi, to lure Koyomi Araragi to the North Shirahebi Shrine. During the confrontation, he revealed an external entity—later revealed as Ougi Oshino—contracted him to eliminate Araragi and Shinobu Oshino. Tadatsuru expressed frustration at feeling like a manipulated pawn, questioning his own motivations. Before he could engage further, Yotsugi Ononoki destroyed his doll body using her "Unlimited Rulebook" ability, an act that deeply affected her. His spirit later appeared in Owarimonogatari's "Mayoi Hell" arc, residing in Avici, a level of Buddhist hell. There, he encountered Araragi after the latter's death, clarifying that Izuko Gaen's assassination of Araragi with the "oddity slayer" sword restored his humanity by purging his vampirism. Tadatsuru confirmed Ougi Oshino's role in contracting him for the assassination attempt, positioning himself as part of Gaen and Oshino's counterstrategy against Ougi. He maintained a detached, resigned demeanor about his existence, freely traveling between the afterlife and the living world via his dolls, though Araragi speculated undisclosed restrictions applied. Visually, Tadatsuru appeared as a pale-skinned man with long blue hair and dark eyes, often clad in traditional white robes adorned with black patterns or a practical apron over a shirt and trousers. His trademark paper cranes functioned as both communication tools and tactical instruments, folded with exceptional speed. Personality-wise, he spoke with flat affect and minimal emotion, openly preferring dolls over human interaction. His actions were driven by aesthetic appreciation for oddities and lingering resentment from his own transformation. He harbored no ill will toward Yotsugi despite their past, even wishing for her to destroy his body, but acknowledged a "sad romance" with Kagenui due to their incompatible natures.