Taiju Unazuki holds the vice presidency of Binan High School's student council as a third-year student, renowned for his naturally handsome appearance and effortless execution of tasks with cool composure. His physical traits include blue eyes and messy blond hair clipped up at the back, paired with an inverted school uniform: black shirt, gray vest, white blazer, black pants, and brown shoes.

Personality-wise, Taiju maintains a smiling facade that typically conceals sadistic inclinations rather than genuine warmth. He excels at identifying others' insecurities and weaponizing them strategically. Despite this manipulative tendency, he shares a notably close bond with Nanao Wakura, rooted in their first-year collaboration operating a soft-serve ice cream booth at the school festival. Their partnership achieved legendary status for its effectiveness, establishing a foundation for their ongoing dynamic as friendly adversaries on opposing sides.

Taiju also developed a strong allegiance to Ata Ibusuki over their high school years. When Ata aligned with Furanui, Taiju followed without hesitation. As Edelstein's oldest member, he views Ata and Maasa Shirahone as "his kids," reflecting a protective yet possessive attitude. He operates as the group's most laid-back member while exhibiting its most pronounced sadistic traits—mirroring Nanao—and uses analytical precision to pinpoint weaknesses, employing lies or manipulation to advance Edelstein's goals.

During Edelstein's conflicts against Happy Kiss, Taiju often observes from the sidelines. His motivations for remaining involve supporting Ata's revenge pursuit and seeking personal entertainment. Furanui implies hidden depths beneath Taiju's superficial persona. As Edelstein faces repeated failures and Ata's frustration escalates, Taiju's concern intensifies, though Ata's reluctance to confide limits him to offering silent support through presence—echoing historical student council dynamics.

When tensions peak between Ata and Kyoutarou, Taiju intervenes proactively, engaging multiple Happy Kiss members simultaneously despite incomplete understanding of their conflict. After preparing to confront Taishi and Ichiro jointly, he resolves the dispute through a one-on-one duel with Nanao. This confrontation reveals his role as Magic Knight Ritter Rosenquarz following his pledge to Furanui.

Overall, Taiju deliberately crafts his external perception like Nanao, with frequent smiles masking calculated or cruel intentions. His development balances loyalty to Ata with amusement-driven engagement in Edelstein's activities, occasionally revealing glimpses of complexity beneath his maintained exterior.