All Soul Reapers possess a , a katana which reflects aspects of the user's soul and personality. A "zanpakutō" has a symbiotic connection with its owner, its spiritual embodiment possessing similar traits to its owner and evolving to reflect its Soul Reaper's power. By learning the name of the sword's spirit, and through training, Soul Reapers can unlock more powerful transformations of their "zanpakutō". The first transformation, known as a which acts like a binding contract between a Soul Reaper and the sword, changes the "zanpakutō"'s appearance to so the owner can facilitate its special abilities to its fullest. The second transformation, known as , is an ability normally seen in Soul Reaper captains that requires ten years minimum to master. Once achieved, the Soul Reaper can unlock the full potential of their "zanpakutō", increasing their own power several times over. Though rare, it is not impossible for two people to manifest the same "zanpakutō" and spirit. This is considered the ultimate taboo of the Thirteen Court Guard Squads and the individuals who manifest the spirit are forced to fight to the death to determine the "zanpakutō"s true master, as in the plot of Bleach: The Diamond Dust Rebellion.