Choo is a fishman and an officer within the Arlong Pirates, serving as one of the crew's primary enforcers during their occupation of the East Blue. As a member of the fishman race, he is naturally endowed with physical strength at least ten times greater than that of an average human, and his body is adapted for underwater combat and mobility. His appearance is muscular and imposing, with notably thick lips, a striped blue vest, a necklace, and sandals, with the mark of the Arlong Pirates tattooed on his right shoulder. Prior to joining Arlong's crew, Choo was part of the Sun Pirates, where he fought alongside other fishmen against the Marines before the crew ultimately fractured.

In terms of personality, Choo presents himself as more composed and cool-headed compared to some of his more hot-tempered comrades. Like his fellow fishmen, however, he holds a deep-seated contempt for humans, viewing them as inherently inferior. This arrogance is a core part of his character and directly contributes to his downfall, as it leads him to severely underestimate opponents he considers weak. He takes pleasure in demonstrating his power over humans and shows little mercy, having participated in the subjugation of entire Marine detachments and the villagers of Nami's home, where he was complicit in the death of Bell-mère. Despite his outward calm, Choo has a breaking point; when pushed or humiliated by a perceived lesser being, he can lose his temper, becoming reckless and more focused on destruction than strategy.

His role in the story is that of a significant obstacle for the Straw Hat Pirates during the Arlong Park arc. He is directly paired against Usopp, the crew's sniper, in a confrontation that serves as a major test of Usopp's bravery. Choo is not driven by a grand personal motivation but rather by loyalty to Arlong and the shared fishman supremacist ideology. His goal is to crush the human pirates who dare to challenge Arlong's authority, and he initially dismisses Usopp as a cowardly liar not worth his time. Key relationships within the narrative include his dynamic with Arlong, whom he follows without question, and with his fellow officers, Hatchan and Kuroobi, with whom he once dreamed of opening a takoyaki (octopus ball) stand before choosing the path of a pirate instead.

Choo possesses notable abilities centered on his unique physiology as a fishman. His primary combat technique involves spitting water from his mouth with incredible force and precision. He is able to fire a single, pistol-like shot called a Water Gun, as well as a more devastating Water Cannon that requires him to first suck in a large volume of water, swelling his body before releasing it as a explosive blast. He can also unleash a rapid-fire barrage of these water bullets, known as the Hundred-Shot Water Gun. In close combat, he has demonstrated proficiency with swords, having wielded a pair of katana during his time in the Sun Pirates.

Throughout his fight with Usopp, Choo undergoes a limited but significant development from the perspective of the antagonist. He begins as a dominant, untouchable force, casually chasing Usopp and threatening the defenseless villagers. His arrogant belief in his own invincibility is gradually eroded as Usopp refuses to stay down, employing trickery, explosives, and hit-and-run tactics. Choo is ultimately defeated not through brute force but through ingenuity, as Usopp covers him in highly flammable alcohol and ignites it, then relentlessly strikes him with a hammer until he loses consciousness. The defeat of Choo, alongside his fellow officers, marks the collapse of Arlong's tyrannical regime over Cocoyasi Village. Afterwards, he is arrested by the arriving Marines, signifying the complete end of his operations in the East Blue.