Kobachi Osaragi is a first-year Shuchi'in Academy student serving on the Public Morals Committee alongside Miko Iino, marked by a yellow armband on her left arm. Her collarbone-length black hair features tied ends resting on her left shoulder, and she wears round childhood glasses obscuring her eyes. Frequent attention from admirers awaits her at the school gate, though her strong confidence in her beauty leaves her unfazed.

Observant and reserved, she speaks sparingly yet perceives astutely, having protected the gullible Miko for a decade. While sharing Miko's sense of justice as a committee member, her approach is less intense. A covert perversion surfaces through confiscated Boy's Love magazines and descriptions of hypothetical "sexual immorality" as "a pretty hot situation." She self-identifies as a social pariah among peers.

Attending Shuchi'in since primary school forged her enduring friendship with Miko, whom she consistently supported during unsuccessful Student Council presidential campaigns. She briefly dated upperclassman Kazeno during culture festival preparations, breaking up weeks later over incompatibility and distaste for his extreme workouts. Supplementary materials note her fatherless family background. Her given name "Kobachi" derives from hiragana components meaning "child," "place," and "blood"; her surname "Daibutsu" (Great Buddha) is atypically read "Osaragi."

Her bond with Miko fractures when Kobachi supports Yu Ishigami's pursuit of Tsubame Koyasu, opposing Miko's feelings for Ishigami. Conflict escalates as Kobachi expresses envy, revealing she believed their friendship stemmed from mutual isolation. After Miko overhears derogatory remarks, their friendship ends temporarily. Reconciliation follows Kaguya Shinomiya's intervention, where Kobachi acknowledges Miko's growth and endorses her feelings for Ishigami.

Unrequited feelings for Ishigami originate from his middle-school defense against unspecified adversity. Without acting on her feelings, she aids his relationship with Tsubame by secretly providing documents detailing Ishigami's past conflict with Ko Ogino, deeming herself suited for such "dirty work" due to social status. She gives Ishigami Valentine's chocolate while accepting non-reciprocation, prioritizing his happiness.

She admires Tsubame for middle-school kindness, driving her support for Tsubame and Ishigami. During student council elections, she assists Miko's campaign against Miyuki Shirogane, delivering a speech that impresses Kaguya. Later, she collaborates with Miyuki as a "chaperone" to improve Ishigami-Miko relations. Her initial rivalry with Kaguya evolves into alliance when both advocate for Ishigami-Tsubame against Chika Fujiwara and Rei Onodera.