Sai is the name of one of the traditional weapons in Eastern martial arts. Due to the specifics of the time, Chinese peasants were forbidden to carry weapons and they were forced to learn to defend themselves with the permitted agricultural implements. Sai, originally used as an agricultural tool for collecting and moving rice straw and hay, later became one of the few permitted agricultural implements suitable for dual use and as a weapon. It is about 50 cm long trident with a significantly longer middle tooth and usually curved outward lateral teeth. The traditional sai has no cutting blades, only pointed tips.

In the Middle Ages, copying from China and the creation of new techniques for fighting sai began on the island of Okinawa. The masters usually carried three sais, one of which was used as a throwing weapon and the other two for fencing. Like most weapons in Kobudo, the sai is used in pairs in each hand. Contrary to popular belief, the usual sai fighting technique is not similar to the knife technique. Sai is often held back to the base of one of the lateral teeth and is used to protect the forearm against sword blows and the lateral teeth as hooks for gripping it. The strokes are mostly poked with the handle, but there are also twists and blocks, very rarely grabbing the handle. Sai katas and punches are very similar to traditional karate. Sai is considered an integral part of the arsenal of most karate styles.