Manabu Naoi, 26, serves as coach for the Nekoma High volleyball team, his alma mater where he played setter seven years prior. During high school, he wasn't a starting member, sharing this experience with Karasuno's Keishin Ukai; they humorously called themselves the "Benchwarmers Club." Physically, Naoi possesses a rectangular head with a jutted jaw, dark short-cut hair, a slight widow's peak, dark eyes, and a stout, muscular build. His personality blends confidence with a competitive streak, particularly evident in his friendly rivalry with Ukai, and he maintains a sense of humor about his non-starting past. Despite his rugged appearance, he struggles with alcohol tolerance. Naoi actively participates in team activities. He acts as main referee during the early Nekoma-Karasuno practice match, reconnecting with Ukai, playfully teasing him about his hairstyle, and referencing their "Benchwarmers Club" history. During the Tokyo Expedition Arc, he observes Karasuno's training innovations at Shinzen High camp and joins nightly social outings with other coaches and Coach Nekomata. His responsibilities intensify during official tournaments. At the Spring High Preliminaries, he encourages Nekoma against Fukurōdani, snaps at Lev's repeated mistakes, and assists with injuries, carrying Yaku off the court and applying ice after Yaku twists his ankle against Nohebi Academy. At the Tokyo Nationals, Naoi focuses on player management. Against Sarukawa Tech and Karasuno, he attempts to motivate a passive Kenma Kozume and later stares in disbelief at Kenma's unusual enthusiasm against Karasuno. He monitors Kenma's increasing fatigue, consulting Coach Nekomata about substitutions to allow rest while acknowledging Kenma's vital, heightened engagement. He also observes team dynamics, like Kuroo calming teammates after Karasuno wins the second set. Naoi appears in the film "Haikyu!! The Dumpster Battle," depicting Nekoma vs. Karasuno at the Spring Nationals. His relationships center on professional ties with Nekoma and his enduring, rivalry-tinged friendship with Ukai, rooted in their shared high school experiences as non-starting setters.