The Gotei 13 (護廷十三隊, goteijūsantai; 13 Division Imperial Guards), otherwise known as the 13 Court Guard Squads, is the organization which most Shinigami join, and one of the three main branches of military in the Soul Society.
The Gotei 13 does not normally operate as a cohesive unit. 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 allocated districts in Rukongai to defend.
The only general authority to call forth a combined front is 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 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 Soul Society doing their divisions' duties, whatever they may be. They are so far spread out, 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 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.
Officially, the Kidō Corps and Onmitsukido are not part of the Gotei 13, but since Suì-Fēng is both the captain of the 2nd Division and the head of the Onmitsukidō, the Onmitsukidō is effectively under the control of the Gotei 13. Additionally, the captain of the Kidō Corps has been known to obey summons and orders from the Captain-Commander of the Gotei 13.
The Gotei 13 is made up of thirteen divisions, 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 Gotei 13 is an organization with a merit-based hierarchy. It has disposed of the system of rank based on seniority. Abilities are the only thing used to determine one's rank.
The captains congregate in the main hall of the First Division Headquarters to discuss important issues involving their specific divisions and matters which 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, 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 answers to is the Central 46 Chambers, who elect the successor of the current Captain-Commander in the event of their death. The former holder of this title is Captain Genryusai Shigekuni Yamamoto of the 1st Division, who had held this post for the last 1000 years.
A Captain 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 leaders of the Kidō Corps and Onmitsukidō possibly being on equal status. All captains are able to utilize the final stage of their Zanpakuto, 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 extensively trained, if not mastered, their Bankai, allowing them to use the enormous power effectively in battle. Most captains are skilled in the use of Shunpo and 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.
They function as chief executive officers, and they 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 (which Kisuke Urahara did upon becoming captain of the 12th Division). Due to captains having supreme authority in their respective division, the divisions are 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 the division in question has no current captain or the subordinate's actions are against the laws or rules of Soul Society.
The true power of Soul Society lies in the captains of the Gotei 13, as they are the leaders of its military arm. With them at full strength, 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: 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 and the least refined of the three. The method is commonly looked down upon by some captains as barbaric compared to the other refined methods. This method allows one to bypass having the mastery of Bankai or other possible abilities which a captain would otherwise be required to have knowledge of, for it allows no judgment from captains who would require those skills as a prerequisite to join their ranks. Though rare in other Divisions, the Eleventh Division has been set up to exclusively utilize this method, with each captain attaining their rank by killing the predecessor.
A Lieutenant, often translated as vice-captain, is the 2nd seated officer in a division. Because captain describes the unit commander, vice-captain is the most literally accurate translation some have used. The manga translation renders the rank as the similar, but somewhat longer "assistant captain", while the English dub of the anime uses the term "lieutenant".