Ougi Oshino appears as a mysterious first-year student at Naoetsu Private High School, claiming to be the niece of Meme Oshino—a claim later disputed by others who assert Meme has no known relatives. Their androgynous look features short black hair, large black irises lacking visible pupils, and strikingly pale skin. They habitually conceal their hands within long sleeves or black gloves. Typically seen in the school's female uniform, Ougi later adopts the male uniform in certain arcs, reflecting identity fluidity. While light novel art sometimes shows them in alternative attire like a black dress, anime adaptations consistently depict school uniforms. This figure displays an enigmatic and condescending personality, materializing during critical narrative moments to manipulate events. Ougi maintains a near-constant smile and speaks with calm precision, showing a keen interest in exposing hidden truths. A recurring catchphrase underscores their role: "I don’t know anything. You’re the one who knows, Araragi-senpai." They declare their purpose is to "punish liars," orchestrating incidents that confront hypocrisy. Ougi exhibits a particular obsession with Koyomi Araragi, criticizing his actions and probing his motivations. Traits include germophobia, a fondness for mystery novels, and occasional detective-like mannerisms. Interactions with Tsubasa Hanekawa are notably confrontational, marked by mutual distrust and rivalry. In reality, Ougi is not human but an oddity—a supernatural manifestation born from Koyomi Araragi’s suppressed self-hatred and guilt. This manifestation began in phases after Araragi encountered the "Darkness," an entity enforcing cosmic order by eliminating aberrations defying their nature. The process solidified when Araragi absorbed a fragment of the Rainy Devil, an aberration granting him the power to manifest oddities. Ougi emerged as the physical incarnation of Araragi’s desire for "divine punishment" for perceived wrongdoings, especially his guilt over failing Sodachi Oikura in middle school. Adopting the Oshino surname deliberately mimicked Izuko Gaen’s prior impersonation of Meme Oshino’s sister. Ougi wields abilities stemming from their vampiric aberration origin: matter creation (generating objects like the ghost classroom), barrier creation (isolating the town from supernatural specialists), and thought manipulation (influencing individuals to accept falsehoods or reveal secrets). Regenerative capabilities, demonstrated when aiding Araragi’s severed arm, support an aura of omniscience enabling event manipulation. Throughout multiple arcs, Ougi acts as an antagonist exposing lies and instigating conflict. In "Ougi Formula," they trap Araragi in a recreated classroom, forcing him to confront repressed memories of Sodachi. During "Nadeko Medusa," they manipulate Nadeko Sengoku into becoming a vengeful deity. "Hitagi End" sees their indirect actions lead to Deishuu Kaiki’s assault. Schemes culminate in "Ougi Dark," where they attempt to destroy Tsukihi Araragi and other "hypocritical" apparitions. Izuko Gaen reveals Ougi’s true nature as a "conventional monster" masquerading as the Darkness. Confronted by Araragi, who identifies them as "Koyomi Araragi," the true Darkness appears to eradicate Ougi for their false identity. Araragi sacrifices his arm to save them. Meme Oshino’s sudden arrival and acknowledgment of Ougi as his niece transforms the false identity into truth, sparing them annihilation. Following this resolution, Ougi adjusts to human life as Meme Oshino’s acknowledged relative. They adopt a more playful demeanor, engaging in pranks like swapping uniforms with Araragi in "Zoku Owarimonogatari." In later stories such as "Orokamonogatari" and "Suruga Bonehead," Ougi interacts with Suruga Kanbaru, offering cryptic guidance without previous vitriol. Their presence at Araragi’s graduation signifies a shift toward integration into ordinary existence, though inherent mysteriousness persists.