Miyabi Nagumo is a tall, fair-skinned student with light blond hair and light blue eyes, considered handsome though some observers note he doesn't match peers like Kiyotaka Ayanokōji. He entered Advanced Nurturing High School in Class B before transferring to Class A via an unspecified method. Nagumo rules with an iron fist, expelling opponents. Former Student Council President Manabu Horikita suspected him of expelling 7 of 12 second-year students. Viewing Manabu as his primary rival, Nagumo repeatedly challenged him to prove superiority and later targeted Manabu's sister Suzune Horikita after she joined the Student Council under his influence. His ideology centers on meritocracy, promising reforms allowing alliances across classes to ascend to Class A. He prioritizes winning larger conflicts over individual battles, exemplified by losing a bet to Manabu yet engineering Akane Tachibana's near-expulsion. Highly persuasive, Nagumo exploits gullible individuals like Honami Ichinose to extract secrets with minimal interaction. He exhibits significant narcissism, viewing others as "toys" to manipulate or sacrifice—such as disclosing Ichinose's secret to Arisu Sakayanagi. He displays attraction toward female students like Ichinose and Suzune Horikita, using premature first-name familiarity and tactics like prolonged physical contact. He attempted to coerce Ichinose into a relationship by offering private points to resolve her class's expulsion crisis, a plan thwarted by Ayanokōji. He later revealed Ayanokōji's relationship with Kei Karuizawa to distress Ichinose, orchestrating encounters to amplify her pain. During the Uninhabited Island Exam, Nagumo employed a "Free Group" strategy directing lower-ranked third-year groups to monopolize points. His group placed second with 325 points, narrowly missing first after Ayanokōji injured him, costing critical time. Nagumo then ordered third-years to surveil Ayanokōji. His overconfidence sometimes causes strategic errors, like confronting Ayanokōji without backup, though he demonstrates calculated planning in events like the Mixed Training Camp. Nagumo collaborated with Acting Director Tsukishiro to create a bounty for Ayanokōji's expulsion, persistently targeting him. He once threatened Kei, prompting Ayanokōji to warn that protection has limits. Nagumo later aided Ayanokōji in expelling Takuya Yagami under the condition of future challenges, revealing his transactional approach to alliances. Retiring as Student Council President, Nagumo challenged Ayanokōji to influence the next presidency, suggesting Honami or Suzune as successors. After Honami declined and Suzune assumed the role, Nagumo tasked her with appointing replacements, affirming his ongoing rivalry with Ayanokōji. Academically and physically highly ranked, Nagumo excels in observation, strategy, and social manipulation. He detected the lack of a designated leader in Ayanokōji's group during the Mixed Training Camp and consolidated control over all third-year classes to mobilize resources. His institutional influence led to systemic changes like the OAA app publicizing student performance metrics and class transfer mechanisms favoring merit-based advancement.