Nami, known as Cat Burglar Nami, is a core member of the Straw Hat Pirates, serving as the crew's navigator. She was the third member to join Monkey D. Luffy's crew and is introduced as a skilled thief and pickpocket with exceptional cartographical, meteorological, and navigational talents. Her driving dream is to draw a map of the entire world, a goal she has held since childhood.

Nami's past is marked by tragedy and coercion. As infants, she and her older adoptive sister, Nojiko, were rescued from a war-torn country by a Marine named Belle-mère, who raised them as her own daughters in the village of Cocoyasi. When the ruthless fish-man pirate Arlong invaded their village, he demanded tribute payments. Belle-mère sacrificed her life to protect Nami and Nojiko. Recognizing Nami's talent for cartography, Arlong kidnapped her and forced her to work for him, making a deal that she could buy back Cocoyasi Village's freedom for one hundred million Berries. For eight years, Nami was driven to steal treasure from pirates to meet this goal, developing a cold, money-obsessed exterior as a defense mechanism while secretly suffering under Arlong's control. When a corrupt Marine confiscated her hard-earned treasure, ruining her chance at freedom, a desperate Nami finally turned to Luffy for help, marking a pivotal turning point in her life.

Personality-wise, Nami is an intelligent, pragmatic, and resourceful individual. She is famously greedy and loves money, a trait born from her impoverished and oppressed childhood, and she often takes control of the crew's finances. Despite this, her loyalty to her friends is absolute, and she will unhesitatingly give up any amount of treasure to protect them. While she often acts as the voice of reason, scolding the more reckless male crew members like Luffy and Usopp, she can also be cowardly, especially when faced with supernatural threats or bugs. Beneath her sharp tongue and materialistic surface lies a deeply caring and protective heart, especially towards her crewmates and children. She is also noted for her high alcohol tolerance and good fashion sense.

Within the Straw Hat crew, Nami's primary role is the navigator, responsible for charting their course through the dangerous Grand Line. Her skills are so refined that she can sense changes in the weather with her body. She has key relationships with each member. She shares a deep, unshakeable trust with Captain Luffy, who freed her from Arlong. She often teams up with the sniper Usopp, who builds and upgrades her signature weapon, the Clima-Tact. She is close with the archaeologist Nico Robin, with whom she shares a bond as the two main female crew members. The cook Sanji constantly fawns over her, which she generally finds annoying but utilizes to her advantage.

Nami undergoes significant character development, transforming from a cynical, isolated thief who hated all pirates into a loyal and integral member of a pirate crew she considers her family. Her initial cold persona is revealed to be a mask for her trauma, and joining the Straw Hats allows her to genuinely pursue her dream of mapping the world on her own terms.

In combat, Nami lacks monstrous physical strength, so she relies on her wits and her evolving weather-based weaponry. Initially using a simple bo staff, she requested that Usopp create a tool for her, resulting in the Clima-Tact. This three-section staff allows her to create and manipulate weather phenomena like bubbles, heat, and cold for offensive and defensive purposes. Usopp later upgraded it to the Perfect Clima-Tact using dials from Skypiea, and after the two-year timeskip, she wields the Sorcery Clima-Tact, which incorporates technology from the weather scientists of Weatheria. A significant power-up occurs when she acquires Zeus, a sentient thundercloud homie originally belonging to the Emperor Big Mom, which she eventually integrates into her Clima-Tact, greatly enhancing its electrical and shape-changing capabilities.