Nami's Weapons
Nami is far from a "power fighter" like Zoro and Sanji, so in battle she makes use of her incredible natural talents at forecasting, as well as a couple of assorted weapons.
The List
Tri-Section Staff
Clima Tact
Perfect Clima Tact
Impact Dial
Tri-section Staff
The first weapon Nami started out using is simple, but remarkably effective for her role as a thief. It consists of three small rods which, when fastened together, form a single staff. It seems strong enough to block iron swords, so for all its utility it also packs some whallop. Nami kept the staff hidden on her person, either on her garter or inside her shirt.
Clima Tact
Usopp is along the same vein as Nami in that he isn't a power fighter, but his genius makes up for that easy. Upon her request he created the original Clima Tact from scratch, delivering it to her in the desert of Arabasta before the big fight began. Simply put, and the Kanji back me up on this, "weather rods" that are the same basic form of weapon Nami wielded before, but with a twist.
There are three Tacts, one each for heat, cold, and electricity. Taken apart their attacks are less than fearsome, but combinations like Cyclone Tempo and Thunderbolt Tempo are capable of bruising and besting the strongest of the strong. The problem lies in Usopp, actually: Half of the original Clima Tact's attacks are pointless party tricks. He even designed the deadly Cyclone Tempo as a boomerang for a gag!
Nami fought with the Clima Tact in two battles, against Miss Doublefinger and against Hotori and Kotori with Gan Fall.
Perfect Clima Tact
After the adventure in Skypiea, Usopp received several Dials. He wasted no time in crafting a better, stronger version of the Clima Tact using them. In this state, there are three orbs that jut off of the staff's length; these are apparently storehouses for the Dials. Thus far, Nami has used the Perfect Clima Tact only during the Enies Lobby battle.
In this state the Tacts are more powerful than ever. Not only do the bubbles come out quicker and smoother, but the power they generate is equally enhanced. Nami has come up with several unique attacks with just one fight, including the illusory Fata Morgana and the piercing Thunder Lance Tempo.
Impact Dial
The Impact Dial absorbs and stores force from whatever strikes it, and at the press of a button releases it in one fell swoop. Its extinct cousin, the Reject Dial, is ten times as powerful. The recoil of the Impact, however, can quite easily break the wielder's arm.
Nami only used the Impact Dial during her fight in Upperyard against Hotori and Kotori, and only because it was available by way of Gan Fall's gauntlet.