Manabu Naoi coaches the Nekoma High School boys' volleyball team at approximately 26 years old. He possesses a rectangular head with a prominent jawline, short dark hair, dark eyes, and a slight widow's peak, coupled with a stout, muscular build. Naoi attended Nekoma High seven years prior, playing as a setter (jersey number 8) but rarely starting, spending most matches on the bench. This shared reserve status with Karasuno's coach, Keishin Ukai, forged a self-deprecating bond, leading them to humorously dub themselves the "Benchwarmers Club." Confident and competitive, particularly in his ongoing rivalry with Ukai, Naoi maintains a sense of humor about his benchwarmer past. His coaching dedication involves practical engagement, like refereeing practice matches between Nekoma and Karasuno. During official tournaments, he actively supports players: encouraging Kenma Kozume to engage more against Sarukawa Tech, showing visible frustration at opponents' defensive tactics, and assisting injured players – carrying Morisuke Yaku off the court and applying ice to his ankle during the Spring High Preliminary against Nohebi Academy. He exhibits attentiveness to player dynamics and fatigue. Observing Kenma's unusual enthusiasm and subsequent exhaustion during Nekoma's national match against Karasuno, Naoi discussed substitution options with head coach Yasufumi Nekomata to preserve Kenma's stamina. He also acknowledged captain Tetsurō Kuroo's leadership in maintaining morale after a lost set. Notably, Naoi has a low alcohol tolerance, which contrasts with his rugged appearance and sometimes embarrasses him during post-practice gatherings with coaching staff. His relationship with Ukai remains collegial, marked by mutual teasing about appearances and competitive banter regarding their teams' future matches.