Manboshi is a merman prince of the Ryugu Kingdom on Fish-Man Island, the third son of King Neptune and Queen Otohime. He is the younger brother of Fukaboshi and Ryuboshi and has a younger sister, Shirahoshi. His rotund, stocky form features brown hair, red fins, and a black polka-dotted merman tail with red scales. He typically wears a blue hat with a serrated white stripe and a yellow sash like his brothers, later adopting a dark shirt during events like the Levely. Highly energetic and unpredictable, Manboshi often breaks into spontaneous song, frequently using the expression "Akkamanbo." This habit began in childhood when he and Ryuboshi used singing and dancing to distract Shirahoshi from emotional distress following their mother's death, showcasing his strong protective instincts toward his sister. As one of the Neptune Army's three primary warriors, Manboshi wields a massive medieval-style longsword with high proficiency. He and his brothers rank as the kingdom's strongest combatants, capable of defeating sea beasts that overwhelmed others. During the conflict with the New Fish-Man Pirates, they initially overpowered the officers until their opponents used Energy Steroids; subduing Manboshi and his brothers required at least two steroids per officer. His sword was later destroyed by Daruma in the anime. Key childhood events shaped him: witnessing a World Noble threaten his mother and seeing Shirahoshi unconsciously summon Sea Kings. After Otohime's assassination, he and Ryuboshi sang to prevent Shirahoshi from crying and triggering another summoning. He later learned of Shirahoshi's latent power as the ancient weapon Poseidon. During the Fish-Man Island Arc, Manboshi investigated illegal entries at Mermaid Cove and pursued the Straw Hat Pirates to deliver a message from Jinbe. Enraged by Hody Jones's coup, he raced with his brothers to rescue their captured father at Gyoncorde Plaza. Overpowered and captured by steroid-enhanced officers, he was rescued by the Straw Hats. He shielded Shirahoshi from Vander Decken IX's knives and blocked a Fish-Man Karate attack from Hody, sustaining severe injuries. Post-victory, he helped imprison Hody and Decken, vowing to strengthen the Neptune Army to repay the Straw Hats. In the Whole Cake Island Saga, Manboshi attended the Levely in Mary Geoise. He expressed joy seeing Shirahoshi experience the surface world and conversed with other royals. When St. Charlos attempted to enslave Shirahoshi, Manboshi and his brothers intervened, ignoring threats to their kingdom, and dodged an attack from Charlos's controlled Bartholomew Kuma. Manboshi reappeared in the Wano Country Saga during the Levely's fourth day, again confronting Charlos and Kuma to defend Shirahoshi.