Chu is a fish-man of the smelt-whiting variety who serves as one of the primary officers in the Arlong Pirates, having previously been a member of the Sun Pirates. He stands out physically with his muscular build, blue skin, and notably thick lips, often wearing a striped blue vest and dark brown pants with his crew's tattoo displayed on his right shoulder.

Among the Arlong Pirates, Chu is generally more composed and cool-headed than some of his comrades. Like his fellow fish-men, he holds a deep-seated belief in the superiority of his own kind and looks down upon humans with contempt. This arrogance, however, proves to be a critical flaw, as it leads him to severely underestimate his opponents. He has a peculiar verbal habit of ending his sentences with a small sound like "chu," which resembles a kissing noise. His personal motivations are closely tied to the ambitions of the Arlong Pirates, as he once advocated for seizing opportunities to build an infamous reputation as a pirate crew.

Chu's history stretches back to his youth, when he, along with fellow fish-men Hatchan and Kuroobi, dreamed of opening a takoyaki shop, a plan they eventually abandoned to pursue a life of piracy. He was part of the Sun Pirates under the legendary Fisher Tiger, and after Tiger's death and the subsequent capture of Jinbe as a Warlord of the Sea, Chu chose to follow Arlong. The crew then established their criminal operations in the East Blue, where they took control of Nami's village and committed numerous atrocities.

In the story, Chu acts as a significant obstacle during the Arlong Park conflict. He initially drags the sniper Usopp back to Arlong's base and later joins his fellow officers in easily dispatching a contingent of Marines. When the Straw Hat crew arrives to challenge Arlong, Chu directly confronts Usopp. Relying on his physical advantages, he easily overpowers Usopp in their first skirmish and believes he has won, leaving his opponent for dead. However, Usopp, driven by shame over his own cowardice, returns to the fight. Through clever tactics involving hit-and-run attacks, a bottle of alcohol, and fire, Usopp manages to wear Chu down and ultimately defeat him by striking him unconscious. Following Arlong's defeat, Chu is arrested by the Marines.

Chu's key relationships are primarily with his fellow fish-men. He has a long history with Hatchan and Kuroobi, having shared both their early dreams and their later criminal path. He is a loyal subordinate to Arlong, adhering strictly to his leader's ideology of fish-man supremacy. He also served under Jinbe during his time in the Sun Pirates, though he was present when the crew debated accepting the World Government's offer to become a Warlord.

As a fish-man, Chu possesses natural physical strength at least ten times that of an average human. His primary method of combat involves spitting powerful jets of water from his mouth. His most basic attack is Mizudeppo, or Water Gun, which fires a single, bullet-like shot. He can increase the rate of fire with Hyappatsu Mizudeppo, the Hundred-Shot Water Gun, which acts like a water-based machine gun. His most powerful technique is Mizu Taiho, the Water Cannon, where he sucks in a massive volume of water to expand his body like a balloon before expelling it all in a single, explosive blast that hits with the force of a cannonball. During his time in the Sun Pirates, he was also seen wielding a pair of katana in battle.