An Explanation of Terms

A zanpakutō is a fictional type of weapon in the Bleach series wielded by those with shinigami powers. The art of using a zanpakutō is called zanjutsu (swordsmanship). The English manga uses the term Soul Slayer in place of zanpakutō, while the anime uses the untranslated term.

Overview

Ordinarily, most zanpakutō look like a like regular katana, with slight variations between them as one would expect between different swords. Under this ordinary exterior, however, lies a sentient spirit. This spirit gives a zanpakutō the power to purify hollows, send souls to the afterlife, and even transform the sword itself into more elaborate and powerful forms. While seemingly similar on the outside, all zanpakutō have unique (though sometimes similar) abilities that usually match their owner's personality.

Zanpakutō, being sentient beings, are a shinigami's partner in battle and cannot be replaced. Because they are alive, a zanpakutō will regenerate if broken, though there is a limit to such regeneration (a vaporized zanpakutō would not regenerate, for example). 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. Because zanpakutō are created with the shinigami that wield them, they tend to have similar personalities.

Forms

BeBeyond their standard sealed state, zanpakutō can manifest themselves in two additional forms, the use of which is dependent upon the shinigami's ability to communicate with and control the zanpakutō's spirit. These two forms, known as the initial release and the final release, are akin to "upgrades" for the zanpakutō, giving it abilities far beyond that of its simple use as a sword. Shinigami usually carry their zanpakutō in the sealed state and activate the released forms as necessary; however, certain shinigami, namely Ichigo Kurosaki and Kenpachi Zaraki, are unable to seal their zanpakutō and therefore carry them in released form constantly.

In addition to the upgraded forms, the sealed form of a zanpakutō can also be radically altered, though such alterations are purely cosmetic and usually don't offer any significant advantage in battle. For example, shinigami who are unable to control their own spiritual power have larger sealed zanpakutō, as Ichigo Kurosaki did when he first became a shinigami. Isshin Kurosaki, Ichigo's father and a former captain in the Gotei 13, explains at one point that high-level shinigami must be capable of maintaining and suppressing the size of their sword. Otherwise, they would end up swinging around swords the size of skyscrapers. Zanpakutō can also be disguised as other objects, though such objects seem to need to be of similar proportions to the sword itself. Kisuke Urahara, for example, disguises his zanpakutō as a cane.

Initial Release
The initial release is the first "upgraded" form available to a zanpakutō. To activate it, the shinigami needs to learn the name of their zanpakutō. This is not as simple as simply picking a name, as the living spirit of the zanpakutō chooses its own name. Therefore, the shinigami must be able to communicate with their zanpakutō effectively. Achievement of the initial release is a mark of expert control of a zanpakutō, and it appears to be a requirement for advancement within the shinigami ranks, as most seated officers and presumably all lieutenants are capable of the initial release. After first learning the zanpakutō's name, the initial release can be performed at will simply by speaking a command followed by the zanpakutō's name. The command phrase varies between users and often relates to the zanpakutō's signature ability. This step may be bypassed by expert shinigami, usually those who are at least approaching discovery of their final release. In rare cases, a zanpakutō, once released, will remain in that state and will not have a sealed state. Such zanpakutō are described as a full-time released form type. Once the initial release is activated, the zanpakutō will change form to access whatever special abilities it is capable of. They usually remain in the form of a sword, but the type of sword differs radically among various zanpakutō. The special abilities of the zanpakutō, like the zanpakutō itself, have specific names that usually must be announced to fully activate the effect. As Ichigo's zanpakutō, Zangetsu, explains, knowing the name of an attack and not knowing it makes a difference in the amount of power that attack has.

Final release
The final release is the second and final form of a zanpakutō. To perform it, a shinigami must be able to materialize their zanpakutō's spirit in the real world and subjugate it, giving the shinigami full reign over the zanpakutō's power. Because such an act usually takes hundreds of years of combat experience to achieve, it is rare amongst shinigami and almost exclusively limited to the thirteen shinigami captains in the Gotei 13. Even among the four noble houses of Soul Society, only one person in several generations will be born with the spiritual power necessary to achieve it. Ichigo Kurosaki and Kisuke Urahara are exceptions to this fact. Using a special device created by Kisuke, which forcibly materializes a zanpakutō spirit (thus bypassing the experience portion of the training), they were able to achieve the same result in three days. After a shinigami is able to material and subjugate their zanpakutō's spirit, the zanpakutō can assume its final and most powerful form. Unlike the initial release, there is no command phrase to activate the final release, though the user will usually say "final release" beforehand. A zanpakutō's final release is often a manifestation of the spirit itself, creating a massive creature or effect to aid the user in battle. Certain shinigami also change with their zanpakutō, gaining different clothing to fit with the form. Most zanpakutō will also gain additional special abilities. Like with the initial release, most of these abilities have an associated name. Maintaining full release is taxing for the wielder, and cannot be held for long periods of time.

Arrancar release
Arrancar, which are hollows that have removed their masks and gained shinigami powers, have zanpakutō and can perform the something similar to a shinigami's initial release called resurrección (Spanish for resurrection). Unlike shinigami zanpakutō, however, an arrancar's zanpakutō doesn't have a true spirit. Rather, it is simply the arrancar's hollow powers sealed into sword form. By releasing their zanpakutō in the same manner as a shinigami, an arrancar can release their hollow powers. Additionally, this seems to be the limit of such a release, as no arrancar has demonstrated any sort of final release form. Because their powers are sealed in their zanpakutō, an arrancar's release will usually transform some or all of their body back into whatever their original hollow forms were, allowing them to use their original abilities. Arrancar can only return to their human form when they reseal their hollow powers; not doing so results in a loss of power comparable to losing a limb. The reason arrancar go through such trouble to seal their power is twofold: it allows them to maintain human form (though it's somewhat obvious they're part hollow) and conserve their power in times of inactivity.

Types

There are several types of zanpakutō, classed by the main purpose or effect of their special abilities. For example, Ichigo Kurosaki's zanpakutō is a melee-type zanpakutō, since it is primarily designed for close-combat. Yumichika Ayasegawa's zanpakutō, on the other hand, is a kidō-type zanpakutō, since it's designed around its special ability rather than its close combat potential. Finally, Rukia Kuchiki's zanpakutō is an elemental-type zanpakutō, since it controls water (more specifically, ice) and uses it to attack.