Helmeppo

Lieutenant Commander Helmeppo is a member of the Marines and the son of the former Marine Captain Axe-Hand Morgan. Prior to joining the military, he was a civilian who took advantage of his father's rank to get what he wanted. However, after undergoing rigorous training with Vice-Admiral Garp, he became a fully-fledged Marine and currently holds the rank of lieutenant commander. Helmeppo is also a member of SWORD, a secret group within the Marines. During the Romance Dawn Arc, Helmeppo's actions paint him as a supporting antagonist. However, he and Koby are the main characters of the Diary of Koby-Meppo Cover Page Serial. In the beginning, Helmeppo was weak and relied solely on his father's status to get by. After training under Garp, he gained exceptional physical abilities, as evidenced by his high jump while intercepting Zoro.

After the two-year timeskip, Helmeppo's skills had grown exponentially, allowing him to single-handedly defeat an entire pirate crew with ease. Helmeppo is particularly skilled in swordsmanship, having even forced Zoro on the defensive for a brief period. Post-timeskip, he has significantly improved his swordsmanship, even causing significant damage to a pirate submarine while underwater. Despite his interest in collecting weapons, including Zoro's Meito, Helmeppo possesses no real desire or ability to use any weapons apart from a single pistol.

Helmeppo, now a full-fledged Marine, carries a pair of kukri as his preferred weapons, which he keeps on his belt at the back of his waist. He first used them in a duel against Zoro in Water 7, but was easily defeated. Following the time-skip, he upgraded to a larger set of kukri. Helmeppo has suggested that he can use Kenbunshoku Haki, noting Koby's remarkable ability to sense an underwater attack on the ships of the Prodence and Dressrosa Kingdoms compared to his own. After the Seven Warlords of the Sea system was disbanded, Helmeppo joined Koby and other Marines in Amazon Lily to arrest Boa Hancock. However, he was turned into stone by Hancock's Mero Mero no Mi power, only to be saved by Silvers Rayleigh's intervention. When Koby was later kidnapped by Marshall D. Teach, Helmeppo and Hibari sought out the help of Prince Grus, a fellow SWORD member and Marine HQ Rear Admiral, to rescue him. Garp then arrived and urged Helmeppo to join him on a mission to Hachinosu to rescue Koby. Helmeppo expressed his frustration at being powerless to stop Koby's abduction, but ultimately agreed to join the mission.