Zanpakutō (斬魄刀, Soul-Cutter Sword; Viz “Soul Slayer”) is the main weapon of the Shinigami, the Arrancar, and the Visored. The Shinigami art of wielding a Zanpakutō is called Zanjutsu (斬術, swordsmanship).
The Zanpakutō of low-ranking Shinigami are called Asauchi and do not have names, but the Zanpakutō of Shinigami of rank have names. In its sealed state, a Zanpakutō has the form of a Japanese sword. Such weapons are unique swords generated from their owner’s souls. Its shape differs depending on its owner.
Zanpakutō are the trademark weapons of the Shinigami. Capable of cutting spiritual bodies, they are among the few weapons which can be used to combat Hollows. Each Shinigami carries a Zanpakutō, and each Zanpakutō is unique: the swords are reflections of a Shinigami’s power and soul, and sentient beings unto themselves. The Zanpakutō’s name is the name of the living spirit which empowers the sword and lends its strength to the Shinigami who wields it. These beings can vary greatly in appearance, and have their own distinct personalities, which match their owner’s.
A Zanpakutō’s shape and abilities are based on their Shinigami’s soul. Once a Shinigami learns his/her sword’s name, they can communicate with one another and grow stronger together. Zanpakutō are born with their Shinigami, and they die along with their Shinigami. Shinigami use them in battle as a reflection of their heart. When released, they can display a vibrant power. They are one with the Shinigami, and they share a Shinigami’s conviction.
Inside each Zanpakutō is an incarnation which manifests itself upon the Zanpakutō’s transformation. The first step is to acquaint oneself with this incarnation.
Zanpakutō that have merged with a hollow also gain the ability to protect their Shinigami through various means. Zangetsu for example was able to manifest a hollow mask to protect Ichigo from major injuries when he was dominated by the Manifestation of Ichigo’s Quincy’s powers. After becoming the dominate spirit, he was able to take possession to Ichigo’s body whenever he was on the brink of death..
An Arrancar’s primary weapon is the same as a Shinigami’s, but unlike a Shinigami’s Zanpakutō, the blade is an embodiment of the Hollow’s power.