Most of the Straw Hat Pirates in One Piece enjoy a good fight, but their navigator Nami is an exception to that rule. In most situations, she prefers to use her wits, and if necessary her feminine wiles, to outsmart opponents.
That said, Nami's knowledge of the weather has made her a formidable fighter when she chooses to be, thanks to her signature weapon, the Clima-Tact. While it's played a big part in getting Nami to where she is now, many fans overlook this unique and useful device.
What is the Clima-Tact?
During the earliest parts of One Piece, Nami is not much of a fighter. While she wields a bo staff, she rarely uses it, preferring to let Luffy and the other Straw Hats protect her. Before the Straw Hats reached the desert kingdom of Alabasta, Nami asked Usopp to make her a new weapon. The result was the Clima-Tact, a three-piece staff that can affect the weather. Nami, whose experience as a navigator makes her a genius at predicting weather patterns, is able to use the instrument especially well.
Over the course of the series, the Clima-Tact goes through many incarnations, gaining power and utility with each upgrade. The mechanism for its use, however, remains largely the same. The Clima-Tact can emit balls of cool or hot air, as well as balls of electricity. By combining these balls, Nami can create an assortment of meteorological phenomena. These include generating mirages, pressurized air, fog, clouds, rain, and most devastating of all, lightning.
Clima-Tact Incarnations
Usopp originally misunderstood Nami and stocked the Clima-Tact with a bunch of useless party tricks, almost similar to a magician's wand. Nami used her own ingenuity to create weather techniques that Usopp had never considered, and did so to defeat the Baroque Works member Miss Doublefinger in her first major battle of the series. After the Skypiea arc, Usopp upgrades the weapon into a truly battle-ready form, which she uses until the time-skip. In Enies Lobby, Nami defeated the CP9 agent Kalifa using the new Perfect Clima-Tact, specifically by generating a bunch of mirage clones of before electrocuting her with the Thunder Lance Tempo.
During the time skip, Nami studies weather in the aptly named Weatheria and upgrades her weapon to become the Sorcery Clima-Tact. This version is much longer than the previous one, being taller than Nami herself when all three pieces fit together. She also gains greater control over the Thunderbolt Tempo, which prior to the time-skip would hit friends and foes indiscriminately.
After they leave Dressrosa, Usopp upgrades Nami's Clima-Tact into the Grow Up Clima-Tact using seeds called pop greens, which also form a large part of Usopp's arsenal. The result is a short, single-piece weapon that can lengthen by being squeezed and subsequently shortened again, not unlike the Power Pole in Dragon Ball. Finally, while in Wano, a sentient thundercloud named Zeus fuses with the Clima-Tact. Zeus was created by a Big Mom's Soul-Soul Fruit and used to be her servant, but joined Nami because he loves eating the thunder balls the Clima-Tact emits. Zeus's soul inhabiting the Clima-Tact makes it capable of shifting into a variety of weapon shapes in addition to having even more powerful lightning-based attacks. Zeus can also act to protect Nami by controlling the weapon of his own volition.
The Clima-Tact is a powerful weapon that has made Nami much more comfortable on the front lines of battle, though she and Usopp still prefer to run from fights if they have the opportunity. It also brings further credibility to Nami's 66 million berry bounty. It's worth noting, however, that the Clima-Tact even at its most powerful has been shown to need several shots to take out tough opponents, and Nami's lack of physical strength forces her to use it primarily as a ranged weapon. In spite of that, the Clima-Tact's unpredictability and variety of uses make it one of the most interesting weapons in all of One Piece.