Yotsugi Ononoki is a tsukumogami-like aberration resurrected approximately fifteen years ago from a human corpse neglected for a century. Members of the Occult Research Club—Izuko Gaen, Meme Oshino, Yozuru Kagenui, Tadatsuru Teori, and Deishuu Kaiki—performed the ritual, which cursed each participant: Gaen in the head, Kagenui and Teori in their legs preventing ground contact, and Oshino and Kaiki in their torsos. A dispute over ownership between Kagenui and Teori ended when Yotsugi chose Kagenui as her master, forging their partnership specializing in immortal aberrations. Yotsugi states she might have preferred Oshino as master given a choice and possesses no memories of her pre-resurrection human life. Physically resembling a twelve-year-old girl, Yotsugi has turquoise hair, green eyes, pointy ears, and pale skin. Her signature attire is a frilly orange dress with a white collar bearing a cross symbol, striped blue and grey stockings, yellow boots, and a distinctive orange hat adorned with googly eyes. After damage from God Nadeko, she temporarily wore a yellow beanie under her orange hat, a green jacket, white shirt, red pants, and black shoes before returning to her original look. When posing as Tsukihi Araragi's doll, she frequently wears a kimono. Yotsugi maintains an expressionless facade and speaks in a flat, monotone voice, often perceived as emotionless. However, she experiences internal emotions but struggles to express them conventionally. To relate to humans, she adopts artificial mannerisms and catchphrases, initially ending statements with "I said with a posed look" while using the masculine pronoun "boku." She later abandons this phrase out of embarrassment and adopts "yay, peace peace" with a peace sign, influenced by interactions. She refers to most characters as older siblings, calling Koyomi Araragi "devilish big brother" due to his vampire ties and Deishuu Kaiki "Kaiki-onii-chan." She uniquely addresses Kagenui simply as "Onee-chan" without honorifics. Despite her stoicism, Yotsugi demonstrates genuine emotional capacity. She considers Koyomi a friend, offering advice from that perspective and expressing reluctance to harm him despite duties. She harbors a rivalry with Shinobu Oshino, frequently mocking her age and holding a grudge from a prior defeat. Over time, she develops contempt for Tsukihi Araragi but forms fondness for Nadeko Sengoku, addressing her with nicknames and acting supportively. Yotsugi is easily influenced and exhibits an appreciation for muscles. During the Mirror World incident, suppressed emotions surface, revealing a more expressive "true personality." She displays wariness toward Izuko Gaen, shivering when held. Her narrative begins as an antagonist in *Tsukihi Phoenix*, working with Kagenui to eliminate Tsukihi Araragi as a Shide no Tori. She attacks Tsukihi using her ability Unlimited Rulebook, provoking Koyomi's rage. After Kagenui concedes defeat following Yotsugi's off-screen loss to Shinobu, their dynamic shifts. In subsequent arcs, Yotsugi becomes an ally, aiding Koyomi against supernatural threats. In *Mayoi Jiangshi*, she questions the purpose of their existences as aberrations. During *Shinobu Time*, she saves Koyomi and Mayoi Hachikuji from the Darkness, transporting them to safety and facilitating their search for solutions. In *Hitagi End*, she acts as Gaen's messenger, warning Kaiki to withdraw from his mission involving Nadeko and bribing him with money. A pivotal development occurs in *Tsukimonogatari* when Koyomi discovers his disappearing reflection, a sign of progressing vampirism. Yotsugi and Kagenui diagnose this as a result of repeatedly letting Shinobu suck his blood to regain powers, particularly during his battles against Nadeko's snake god form. Kagenui gives Koyomi an ultimatum: abstain from vampire abilities or lose his humanity. Later, Tadatsuru Teori kidnaps Suruga Kanbaru, Karen Araragi, and Tsukihi to lure Koyomi. At the North Shirahebi Shrine, Teori refuses to fight, claiming their roles are "cast" by external forces, and asks Yotsugi to kill him. She obliges, obliterating him with Unlimited Rulebook, explaining "I am a monster," which traumatizes Koyomi and alters their relationship. To counter this distancing, Gaen and Kagenui assign Yotsugi to live with the Araragi family as Tsukihi's doll, protecting Koyomi and monitoring the town. In later stories, including the Off & Monster Season arcs, Yotsugi remains embedded with the Araragi household. She investigates, monitoring Tsukihi's mystical nature. When Tsukihi discovers Yotsugi is sentient, Yotsugi fabricates being a magical girl from another world, enlisting Nadeko's help to maintain the ruse. She assists Nadeko's recovery from her snake god ordeal and supports her manga artistry ambitions. Yotsugi suggests Nadeko create four self-representing clones to accelerate creation, but the clones escape, forcing Nadeko to confront her fractured identity. Yotsugi continues collaborating with characters like Mayoi Hachikuji to resolve supernatural incidents, reflecting her ongoing role as a problem-solver. Yotsugi's primary ability, Unlimited Rulebook, manipulates spatial and physical properties. She expands her finger to unleash destructive blasts capable of obliterating humans or structures and propels herself vertically at high speeds for precise long-distance travel, enduring intense pressure during transit. She possesses significant physical strength, effortlessly carrying humans on her fingertip, classifying her as a formidable combatant among aberrations.