Nezumi is the Marine Captain of the 16th Branch of the East Blue's Marine Branch. He was incredibly corrupt and, in exchange for bribe money, he covered up the majority of Arlong's activities in the Conomi Islands.
First Appearance in Anime
One Piece Episode 31
Tamotssu Nishiwaki (Japanese), Dan Green (English)
Marines, Marine 16th Branch
In exchange for monthly monetary payments, Nezumi and his group willfully disregarded the Arlong Pirates' rule over the Conomi Islands for a while. Nezumi usually made sure to spend as little time as possible at Arlong Park, in part because he found the Fish-Men to be uncomfortable, despite the fact that Arlong took great pleasure in the arrangement and regarded the Marines to be "honored guests."
After a normal payout one day, Arlong alerted Nezumi about a hidden treasure: the money and treasures that Nami had been stowing away for eight years in order to buy her release from Arlong. Nezumi gladly led his squad there and commandeered Genzo to bring them to Nami's home because he knew the treasure was classified as stolen goods. Genzo, Nojiko, and especially Nami were furious when the Marines raided the entire farm with the sole purpose of seizing Nami's labors.
Nami and her guardians were incensed when they learned that the Marines were working with Arlong, so Nezumi gave the order to use force. While Nami and Genzo were unharmed, Nojiko was shot in the waist. Soon later, Nezumi discovered the trove, which numbered 93,000,000 berries in all, and reveled in it, unaware that his actions had driven Nami and Genzo to the brink of exhaustion.
Because of their desperate tactics, the Straw Hat Pirates would eventually invade Arlong Park and entirely destroy the Arlong Pirates. Nezumi attempted to sabotage the Straw Hats' victory after seeing Arlong Park fall in order to take both the glory and the money from Arlong's personal funds for himself.
However, Roronoa Zoro and the other Straw Hats soundly defeated him and his squad before Nami herself "requested" that he return the stolen money and aid the surrounding population in their recovery from Arlong's rule. Nezumi swiftly consented, feeling helpless and afraid, then retreated to a safe distance before pledging vengeance on the Straw Hats' leader Monkey D. Luffy.
Later, Nezumi went back to the Branch 16 headquarters and informed his supervisors of the occurrence; much to his chagrin, his subordinates could only provide a picture of Luffy grinning absolutely innocently. Despite this, the revelation caused Marine Headquarters to place an extraordinary 30,000,000 berry reward on Luffy's head.
Nezumi is as craven, opportunistic, and wholly lacking in integrity as his mouse-like looks would have you believe. His need for money is so intense that it will drive him to form permanent alliances with criminals, hide his hatred for Fish-Men personally, and even engage in outright violence against humans. If he is defeated, he will instantly crouch and beg until he is able to flee to a safe distance. Normally, he radiates a smug, supercilious look, expecting his status to force respect and obedience.
Nezumi is a small, dark-haired man who has a distinctly mouse-like look, fitting for a character with that name. He has a tiny goatee and six long, wire-like whiskers on his top lip, and his eyes are permanently contracted. His Marine uniform has been drastically changed; the regular helmet has been replaced with a mouse-eared cowl, and it is attached to a greatcoat that buttons up to his feet and is embellished with a belt and blue epaulets.
Nezumi is in charge of the 16th Branch and commands a number of armed subordinates as a Marine Captain. He hasn't shown any personal combat prowess and instead seems to rely completely on his status to repel threats. At most, he can swim well enough to make it out of Arlong Park's harbor.
Nezumi is seen using a handgun and seems to be able to use it rather well.
Nezumi is not only an anime character but is also a video game character:
One Piece Treasure Cruise
Set Sail Pirate Crew!
One Piece: Pirates Carnival
One Piece: Become the Pirate King!
Aim! The King of Belly
One Piece: Grand Battle! Rush!
One Piece: Dragon Dream!
One Piece: Grand Adventure