Nadeko Sengoku is a central character in the Monogatari series who appears throughout its many arcs, including the Off & Monster Season adaptation. She is introduced as a second-year middle school student and a childhood friend of Tsukihi Araragi, also becoming acquainted with Tsukihi’s older brother, Koyomi. In her earliest appearance, she is presented as a shy, reserved girl who often looks downward, wears her bangs long over her eyes, and carries a waist pouch. She is easily amused and deeply protective of her forelocks, which she regards as more important than her modesty.

Nadeko’s background is marked by her involvement with a curse called the Snake Constricting Rope, which manifests as an invisible snake coiling around her body and leaving scale-like scars. This curse was inflicted by classmates as a result of romantic rejection and jealousy. Koyomi helps her remove it, and she develops intense feelings for him, referring to him as “Koyomi onii-chan.” Over time, her personality is revealed to be far more complex than her timid exterior suggests. In the Nadeko Medusa arc, she discards the victim role and reveals an obsessive, egotistical, and manipulative side, becoming a destructive snake deity enshrined at North Shirahebi Shrine. She intends to kill Koyomi out of unrequited love but is ultimately convinced by Kaiki Deishu to move on and pursue a career as a manga artist, a dream she had kept hidden.

Later, in the Koyomi Reverse arc, Nadeko’s character further deepens as she adopts a boyish, brash, and rude mannerism—echoing the personality of the snake entity Kuchinawa that once influenced her. She expresses regret over this hidden part of herself, showing internal conflict over her identity. In the Off & Monster Season, specifically the Nadeko Draw arc, Nadeko is now a third-year middle school student living at home and devoting herself to painting with the goal of becoming a professional manga artist. Her parents give her an ultimatum: if she cannot achieve something concrete by graduation, she must leave the house. Under pressure, she chooses to create four shikigami versions of herself—dubbed the Four Nadeko Senjougahara—to help her meet her deadline and explore different aspects of her personality. With the assistance of Yotsugi Ononoki, she confronts her own uncertainties about youth, identity, and the future, ultimately seeking a path that is truly her own.

Nadeko’s notable abilities are tied to her history with snakes and her former divine status. She can manipulate or create snake-related curses and, as an ex-god, retains some supernatural influence. In the Off & Monster Season, she demonstrates the ability to generate shikigami that embody different facets of herself. Key relationships include her unreciprocated romantic attachment to Koyomi Araragi, her long-standing friendship with Tsukihi, her collaboration with Yotsugi Ononoki, and her brief interactions with Ougi Oshino, who accompanies her to her old middle school. Her development traces a journey from a quiet, seemingly helpless girl into a morally ambiguous figure who must reconcile her past actions and hidden desires with the person she wants to become.