The Gotei 13 (護廷十三隊, Goteijūsantai; 13 Division Imperial Guards, 13 Court Guard Squads in the English dub, 13 Court Guard Companies in the English manga) is the primary military branch of Soul Society. It is also the main military organization that most Shinigami join after the academy.

Mission

The Gotei 13 serves as a military force with its primary responsibilities consisting of:

The defense of the Seireitei, the center of Soul Society.
The deployment of Division members into enemy territory for combat operations.
The deployment of Task Forces as defensive measures in the world of the living.
The guiding of souls to the Soul Society.


General Operations:

The Gotei 13, in contrast to the normal operations of modern-day militaries, does not operate as a cohesive unit normally. The command of the divisions are generally left to the discretion of its particular Captain, who commonly runs it whatever way he or she sees fit, allowing for the change of a division's traditional duties to an entirely new set and even the creation of a separate institution connected to the division. The Gotei 13's main duty is to defend the Seireitei but they are also allocated districts in Rukongai to defend. In addition to these duties, Shinigami also have to deal with the business of being assigned to the Human World.

The only general authority to call forth a combined front would be that of an edict from the Central 46 Chambers, or more often the Captain-Commander. It is not uncommon for captains to not see each other as a whole group for long periods of time, except for cases involving a threat to all of the Soul Society, a captain's punishment, or to a lesser degree, a captain's promotion. On a regular basis, the captains are spread out all across the Soul Society doing their divisions' duties, whatever they may be. They are, in fact, so far spread out that getting the Captains together as a group, or even getting their lieutenants together as a group, could normally take a day to accomplish.

Unless specifically ordered by the Captain-Commander, captains can choose whether or not to attend meetings (at their own risk) or not even involve themselves in the daily situations of the Soul Society. Captains are not allowed, without permission, to carry out activities outside of their normal jurisdiction or their division. The captain of one division cannot punish the subordinates of another captain.


Structure

The Gotei 13 is made up of thirteen components: They are split into thirteen divisions (hence the name), with several divisions having certain specializations.

The Gotei 13 is led by the "Captain-Commander", who has the statuary authority to conduct all the affairs of the Gotei 13; while deferring to the authority of the Central 46 Chambers in matters involving Soul Society.

As with any army, the Gotei 13 has ranks. There are 20 ranks for officers but no ranks for non-officers. The lower the number is, the higher the rank. The ranks and their descriptions are below, from highest to lowest in terms of strength. The Court Guards are an organization with a merit-based hierarchy. They have disposed of the system of rank based on seniority. Abilities are the only thing used to determine one's rank.
Captain's Council

The Captains congregate together in the main hall of the First Division Headquarters to discuss important issues involving their specific divisions and matters that affect Soul Society. This council is highly formal with the captain-commander leading its proceedings. All captains are considered equal (with the exception of the captain-commander) and determine the course of their individual division unless dictated otherwise by the captain-commander. Votes are carried out via a unanimous consensus.

The Captain-Commander (総隊長, Sōtaichō; Viz "Captain-General"; Captain-Commander, Head-Captain in the English dub) is the supreme leader of the Gotei 13. The position requires the Captain-Commander to oversee the overall operations of the Gotei 13, Onmitsukidō and Kidō Corps when the well being of Seireitei and Soul Society is at stake. The only power the Captain-Commander is answerable to is the Central 46 Chambers.

A Captain (隊長, Taichō; lit. Unit Commander) is the leader of one of the thirteen divisions (with the special case of the Captain-Commander).

Captains are generally the most respected Shinigami within the Soul Society, with the Kidō Corps, and Onmitsukidō leaders possibly being on equal status. All captains are able to utilize the final stage of their Zanpakutō, and are far more powerful than even their lieutenants. Knowing Bankai gives captains an average of five-to-ten times the strength of Shinigami who are unable to perform it. They have also extensively-trained, if not mastered, their Bankai, allowing them to actually use the enormous power effectively in battle. Most captains are also skilled in the use of Flash Steps, Kidō, and generally have extensive knowledge of Shinigami history and battle tactics. All of these factors create a vast power-gap between captains and lower-ranked officers.

Captains determine the course, organization, tactics and policy of their division. The power a captain has over his/her division is absolute and cannot be questioned by subordinates or the captains of the other divisions. A captain can choose to change the division specialty. Due to captains having supreme authority in their respective division the divisions have become separate entities and not a cohesive military. In this way they only have the right to punish the actions of their subordinates and not those of other divisions unless in the instance that the division in question has no current captain or the subordinates actions are against the laws or rules of Soul Society.

Although not commonly stated, the true power of the Soul Society lies in the captains of the Gotei 13, as they are the leaders of its military arm. With them at full strength, the Soul Society is safe and almost unbeatable. If they are broken, their strength dwindles, making them highly vulnerable.

There are three different ways to become a Gotei 13 captain:

Captain proficiency test (隊首, taishu): A test which requires the ability to perform Bankai. Nearly all Shinigami become captains using this method. At least three existing captains, including the Captain-Commander, have to witness the test.
Personal Recommendation: To have personal recommendations from at least six captains and approval from at least three of the remaining seven.
Trial by Combat: To defeat a captain one-on-one with at least 200 witnesses from the captain's division. This method is seen as being the exceedingly rarest of the three as well as the least refined. The method is commonly looked down upon by some captains as barbaric compared to the other refined methods. This method also allows one to bypass having the mastery of Bankai or other possible abilities that a captain would otherwise be required to have knowledge of, as it allows no judgment from captains who would require those skills as a prerequisite to join their ranks.

Lieutenant

A lieutenant (副隊長, fukutaichō; Viz "Assistant Captain"; vice-unit commander, often translated as vice-captain) is the 2nd seated officer in a division.

Lieutenants function as executive officers for their division, taking care of or supervising day-to-day operations. They (along with their captains) are not assigned to one specific squad. They generally only know the Shikai of their Zanpakutō, but are still the second strongest in their division. In the case of a division captain's death, departure, or other circumstances making him unable to perform their duties, the lieutenant acts as the "substitute captain" until another can be assigned.


Seated Officers

Seated officers are the remainder of the officers in the Gotei 13 that hold ranks at or below 3rd Seat. Captains and lieutenants have the ranks of 1st and 2nd Seats, respectively. Next to that, there are 18 more seats (3rd-to-20th). These ranks are somewhat analogous to junior officers or non-commissioned officers in modern military. There seems to be a distinction between senior and junior seated officers, just like in real-life armies. In the Gotei 13, only one person can hold a senior officer rank (such as 3rd or 5th seat), but there are several holders of junior officer ranks (e.g. 20th seat). This may vary from division to division however. Seated officers often lead subunits within each division.