Sentomaru first appeared as a large, stocky man resembling a sumo wrestler, marked by a distinctive scar running from his left eye to the corner of his mouth – a remnant of youthful battles with wild bears. His attire featured a brown bib-like shirt emblazoned with a "heaven" emblem and the red-and-white rope of a sumo champion, complemented by arm bandages and a "battle" kanji tattoo on his left shoulder. He wielded a massive double-edged axe. Following a two-year timeskip, he adopted a Marine officer's coat, removed the bandages, and presented a bulkier physique. Abandoned by his village in childhood due to violent behavior, Sentomaru survived alone in the mountains, defeating bears using sumo techniques. Dr. Vegapunk discovered him during a Marine investigation into bear attacks and, impressed by his strength, offered him a position as his bodyguard. This role provided stability and forged Sentomaru's unwavering loyalty to Vegapunk. He later joined the Marines' Science Unit as its captain, commanding Pacifista units and collaborating closely with Admiral Kizaru, whom he respectfully called "uncle" despite no familial relation. Kizaru trained him, though Sentomaru frequently expressed frustration at the Admiral's lack of restraint. During the Sabaody Archipelago arc, Sentomaru confronted the Straw Hat Pirates, utilizing Armament Haki to repel Luffy's attacks and damage his rubber body. He coordinated Pacifista units and Kizaru during this operation. He subsequently participated in the Summit War at Marineford, deploying Pacifistas against pirates under Fleet Admiral Sengoku's orders. After the timeskip, now a full-fledged Marine officer, he returned to Sabaody to apprehend the returning Straw Hats. There, he witnessed Luffy's growth, including the use of Haki to destroy a Pacifista, and dismissed an impostor claiming to be Luffy as unworthy. In the Egghead Incident, Sentomaru prioritized his loyalty to Vegapunk over the Marines. When CP0 agents attacked Vegapunk, he assumed command of Seraphim units to defend the scientist. Stabbed through the chest by CP0's Rob Lucci, he activated Mark III Pacifista units to aid Vegapunk's escape, citing fears of a repeat of the Ohara incident. He later confronted Admiral Kizaru, who defeated him on orders from Jaygarcia Saturn. Despite severe injuries, he survived, escaped Marine custody amid chaos, and fled Egghead in a small boat. In the non-canon film *One Piece: Stampede*, Sentomaru appeared during the Pirates Festival on Delta Island. He commanded Pacifistas to arrest participating pirates and reacted to the arrivals of Warlords Dracule Mihawk and Boa Hancock. When the festival escalated due to Douglas Bullet's siege, he coordinated with Marine forces but was incapacitated by Perona's Negative Hollow abilities. Sentomaru claimed the "world's tightest defense," employing Armament Haki to deliver powerful open-palm strikes inspired by sumo, like the "Ashigara Dokkoi," capable of injuring Devil Fruit users without direct contact. He wielded his axe against formidable opponents such as Chopper's Monster Point. His perceptiveness allowed him to recognize advanced Haki usage in others, including Luffy's post-timeskip capabilities.