Shinigami.

Synopsis;

Shinigami are souls that have manifested reiatsu (spiritual energy) and are capable of evoking an extension of their very soul in the form of a zanpakutou (sword) with unique abilities derived from the individual's spiritual essence. Out of the numerous tasks appointed to Shinigami, the three most noteworthy are as follows:

1.) Monitoring the balance between Soul Society and the Earth.

2.) Seeking and destroying Hollow whenever possible.

3.) Finding human souls which haven't passed on, due to the circumstances of their death or their own fear of what may lie beyond death.

General;

Souls who aspire to become Shinigami must attend periodic entrance exams at the Pure Sanctum. If they meet the criteria to become potential Shinigami, they're sent to an Academy School, where they learn all the prerequisites of the occupation and are drilled on the content. Graduates of the Academy are guided through manifesting their own Zanpakutou and how to unlock its abilities (each Zanpakutou has the potential of two additional forms; Shikai and Bankai).

Shinigami that show promise are drafted into one of 13 Gotei, each squad having their own primary function (as an example, the 11th Gotei specializes in combat). Though no set number limits the squad's growth, only the top ten members are ranked. Seats 10 - 3 are ranked as such (8th Seat, 7th Seat, et cetera), though the prominent two members of the squad are set apart from the rest as commanding officers. What would be 2nd Seat is known as the Lieutenant, or "Vice Captain," of the Gotei. The 1st Seat is given absolute command as the squad's Captain.

Captain class Shinigami are renowned throughout Soul Society, baring the most fortitude and have transcended far above mediocrity. They are revered and deferred to by all others, generally being viewed as the best Shinigami Soul Society has to offer.

Zanpakutou;

In essence, a zanpakutou is the manifested weapon of a Shinigami's very soul. The sword itself seems like a traditional katana at first glance, though many have unique cross-guards portraying the wielder them self. Dwelling within the zanpakutou is its own spirit, a guiding force that reaches out to the wielder who gave it birth and lend aid.
The wielder may allow the zanpakutou to absorb his reiatsu and in return, the spirit can unleash its special abilities as well as amplify the Shinigami's power.

Every zanpakutou has the first form, as well as the potential to attain three others:

Shikai:

The second form of a zanpakutou, usually changing the appearance of the sword (sometimes into a completely different structure), as well as giving it a giant boost in power. Each Shikai form has its own ability, which must be earned through communicating with the spirit dwelling within the zanpakutou. This process is to earn the trust and respect of the spirit, which in turn reveals its name to the wielder.

Note; Shikai is reserved for Captain- and Lieutenant-class Shinigami, though the highest Seats of a Division may be alotted this ability if they have proven their capacity to seven Captains.

Bankai:

The third form of a zanpakutou, considered the pinnacle of Shinigami power. This is the true form of a zanpakutou, revealing a new and (generally) incredibly powerful ability. Again, its usual for the zanpakutou to change shape into something new altogether. The ability to envoke the Bankai state lies within being trusted and respected by the spirit within the zanpakutou, co-existing in a perfect harmony.

Note; Every Shinigami who has attained Bankai has been recorded in the history of Soul Society without exception, and is held in utmost esteem. Bankai is reserved for Captain-class Shinigami, and Lieutenants who show a high aptitude and have proven themselves to seven Captains.

Senkei:

A zanpakutou transformation which transcends Bankai, extending a Shinigami's power even further with its capability. Exceptionally powerful Captain-class Shinigami have been known to portray abilities unique to themselves and their zanpakutou, and this manifestation is known as ''Senkei.''

Note; Senkei is an extremely rare ability, and will only be granted to Captain-class Shinigami who have proven themselves and their capabilities to the Captain Commander.