Miko Iino enters Shuchiin Academy as a first-year student, first serving on the Public Morals Committee before becoming the Student Council auditor. Raised in a strict household by a Supreme Court judge father, she absorbed law and justice texts from a young age, forging her intense dedication to rules and public morals. This family background fuels her serious demeanor and academic focus.

Highly disciplined and morally rigid, Miko strictly enforces school regulations. She frequently interrupts Student Council activities, criticizing members like Kaguya Shinomiya and Miyuki Shirogane for perceived improprieties, creating tension. Yet beneath this stern exterior lies social naivety and a suppressed curiosity about taboo subjects. She secretly listens to "Self Confidence Boosting" ASMR recordings featuring male praise. Her interest in binaural audio surfaces during a cultural festival horror house; her recorded reactions in a bondage-like scenario reveal a sensual side she struggles to reconcile with her public image.

Academically, Miko ranks among Shuchiin's top students due to diligent study and deep legal knowledge, though her social intelligence lags. She initially views Shirogane negatively as corrupt, idolizing his Spider-Man alter ego instead, highlighting her "Hates My Secret Identity" trait.

Her relationship with Yu Ishigami forms a significant arc. Former middle school classmates, their dynamic involves constant conflict stemming from her disciplinary role and his rule-breaking. Despite antagonism, they secretly assist each other: Ishigami removes derogatory signs from her back and defends her dignity during elections; Miko protects him from suspension, citing his academic efforts. Neither acknowledges these acts initially, believing help should be given without expectation. Miko develops romantic feelings after discovering his kindness, like gifting her photos of a missed bonfire with a heart-shaped lost item. Jealousy surfaces when he dates Tsubame, and their relationship evolves through shared moments like bonding over video games, where he notices her previously unseen supportive side.

Integration into the Student Council facilitates Miko's gradual development. While acting as a grounding force against council antics, the group helps loosen her rigidity. Participating in social activities, such as taking humorous filtered photos, reduces her "seriousness points," marking growth toward balancing discipline with relatability. Interactions reveal vulnerabilities, like stage fright overcome through Miyuki's impromptu debate challenge, reigniting her competitive spirit and restoring confidence.