Yotsugi Ononoki is a tsukumogami created from a human corpse resurrected approximately fifteen years before the main events via a forbidden ritual performed by the Occult Research Club. This club included Izuko Gaen, Meme Oshino, Deishuu Kaiki, Yozuru Kagenui, and Tadatsuru Teori. The taboo ritual cursed each participant: Gaen in the head, Kagenui and Tadatsuru in their legs, and Kaiki and Oshino in their torsos. Conflict over her ownership arose between Kagenui and Tadatsuru after her creation, resolved when Yotsugi chose Kagenui as her master, forging their partnership as specialists targeting immortal aberrations. Her family name "Ononoki" incorporates the "Ki" from Kaiki's name. Introduced as an antagonist in the *Nisemonogatari* "Tsukihi Phoenix" arc, she and Kagenui pursued Tsukihi Araragi, an immortal Shide no Tori. Yotsugi attacked Tsukihi using her ability, "Unlimited Rulebook," provoking Koyomi Araragi's rage. Following a compromise, she battled Shinobu Oshino off-screen and lost, leading to her and Kagenui's retreat. She subsequently transitioned into a recurring ally, eventually residing with the Araragi household as Tsukihi's "doll" to protect Koyomi under Gaen and Kagenui's arrangement. She maintained this role until her departure, after which she frequently partnered with Nadeko Sengoku. Her appearance resembles a twelve-year-old girl with cyan hair tied in twintails, lime green eyes, pale skin, and pointed ears. She typically wears an orange-and-red frilled dress, striped blue-gray stockings, yellow rain boots, and an orange hat featuring googly eyes. While staying with the Araragi family, she often wore Tsukihi's kimono. After her hair was cut shorter in *Nademonogatari* following an encounter with God Nadeko, she temporarily adopted a new outfit: a green jacket, white shirt, red pants, and a yellow beanie under her signature hat, though she later reverted to her original look. Yotsugi exhibits an expressionless demeanor and monotone speech, initially suggesting emotional absence. However, this stems from an inability to express emotions conventionally. Her personality adapts to those around her, resulting in evolving mannerisms. Early on, she frequently used the masculine pronoun "boku" and ended statements with "I said with a posed look," a phrase she later abandoned out of embarrassment. In *Koimonogatari*'s "Hitagi End" arc, she adopted a peace sign gesture and the phrase "Yay, peace peace." She refers to others as older siblings, calling Koyomi "oni no onii-chan" (devilish big brother) due to his vampiric ties and addressing Kaiki as "Kaiki-onii-chan." Despite her stoicism, she demonstrates complex emotions. She considers Koyomi a friend, offering advice "as a friend" and expressing reluctance to harm him despite her duties. She holds a grudge against Shinobu, mocking her age as "Old Lady," while also fearing her power after their prior defeat. She developed contempt for Tsukihi Araragi but shows deep fondness for Nadeko Sengoku, supporting her through personal challenges, including housing issues after Nadeko's parents demanded she move out post-graduation. Yotsugi aided Nadeko by modeling for manga sketches and seeking solutions through Gaen, though she framed this as self-interest to avoid the Araragi household. Her primary ability, "Unlimited Rulebook," enables varied feats such as enlarging her finger into a destructive hammer-like weapon or propelling herself or others at high speeds for travel. She also possesses superhuman strength, allowing her to carry humans effortlessly. In *Zoku Owarimonogatari*, the Mirror World incident forced her suppressed emotions to surface, revealing a more expressive "true personality." She narrates arcs like *Orokamonogatari*'s "Yotsugi Future" and stars in titular arcs including "Yotsugi Doll," "Yotsugi Buddy," and "Yotsugi Shadow." Her character explores themes of purpose and coexistence; she questions why she was revived and strives to live among humans despite her nature. She reads parody magazines like *Agajiso*, a wordplay on *Shonen Magazine*.