One Piece is a long-running shonen action series whose combat system underwent a few phases of evolution. At first, typical pirate weapons like cannons, swords, and musket pistols were impressive, but then the Devil Fruits took over the combat system, especially in the Grand Line. Then, the Haki combat system joined the fray, mostly to help non-Fruit users stand a chance.
Source：https://www.cbr.com/one-piece-best-color-arms-haki-users/
