The Zanpakutō of low-ranking Shinigami are called Asauchi and do not have names, but the Zanpakutō of high-ranking Shinigami do have names. In its sealed state, a Zanpakutō has the form of a Japanese sword.[1] Such weapons are unique swords generated from their owner's souls. Its shape differs depending on its owner.[2]
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 are similar to their owner's.
A Zanpakutō's shape and abilities are based on their Shinigami's soul. Once a Shinigami learns his/her Zanpakutō'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.[3]
The only known exception to how a Zanpakutō is unique to the Shinigami carrying it is the Shinken Hakkyōken, in which it is a Zanpakutō passed down from one generation to another of the Ise Clan. Because they are bound to this blade, it is impossible for members of the family to create their own unique Zanpakutō.[4]
Inside each Zanpakutō is an incarnation which manifests itself upon the Zanpakutō's transformation. The first step is to acquaint oneself with this incarnation.[5]
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 powers.[6][7] After becoming the dominant spirit, he was able to take possession of Ichigo's body whenever he was on the brink of death.[8][9]