Each Zanpakutō is a manifestation of its owner's soul, and has a unique name which is required for a shinigami to learn in order to use Shikai and Bankai. As such each Zanpakutō has unique abilities that match their owner's characteristics and personality, and their names usually hint to what these powers may be. A Zanpakutō spirit is part of its owner's soul, and often share the same personality traits. At the same time, they are also independent, and thus can be considered a Shinigami's partner in battle. Because they are part of their owner's soul, a Zanpakutō cannot be replaced, though it will slowly regenerate if broken. As a Shinigami gains power, their Zanpakutō can change form by allowing the inner being to manifest itself to a greater degree in the outside world. The sword and the inner being are synonymous to each other. No matter what form (or size) a Zanpakutō takes, it is always virtually effortless for its owner to wield because it is a part of its owner's soul. On the other hand, it is much more difficult for a Shinigami to wield a Zanpakutō that is not their own; Kaname Tōsen is the only known Shinigami so far to actually do such a thing. Most Zanpakutō look like regular katana, with slight variations between them as one would expect between different swords. Each Zanpakutō has the power to send pluses to the afterlife, purify Hollows, and transform the Zanpakutō itself into more elaborate and powerful forms. Not all Shinigami can hear the name of their Zanpakutō and thus can not achieve the higher tiers of power.
Arrancar, are Hollows that have removed their masks and gained Shinigami powers, have Zanpakutō and can perform something similar to a Shinigami's release called Resurrección ((帰刃（レスレクシオン, resurekushion; Spanish for "resurrection", Ja[anese for "returning blade). Unlike a Shinigami's Zanpakutō, however, an Arrancar's Zanpakutō is simply the Arrancar's Hollow powers sealed into the shape a of sword. By releasing their Zanpakutō in the same manner as a Shinigami, an Arrancar can release his or her Hollow powers.
Because their powers are sealed in their Zanpakutō, an Arrancar's release will usually transform some or all of their body into a Hollow-like form, allowing them to use their abilities freely. This form usually reflects what the Arrancar looked like as a Hollow, although to highly varying degrees. Arrancar normally only return to their human form when they reseal their Hollow powers; doing so without resealing, though possible, is a permanent change comparable to amputating a limb. The reason Arrancar go through such trouble to seal their power is twofold: it allows them to maintain human form and conserve their power in times of inactivity.