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.
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 (, 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. The current holder of this title is Captain Genryūsai Shigekuni Yamamoto of the 1st Division, who has held that post for the last 1000 years.
■A Captain (, 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. With one exception, 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 (As Kisuke Urahara did upon gaining command). 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
1.Captain proficiency test (, 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.
2.Personal Recommendation To have personal recommendations from at least six captains and approval from at least three of the remaining seven.
3.Trial by Combat To defeat a captain one-on-one with at least 200 witnesses from the captain's division. Kenpachi Zaraki is the only known current captain to have achieved his rank using this method. 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.
■A lieutenant ( "Assistant Captain"; vice-unit commander, often translated as vice-captain) is the 2nd seated officer in adivision.
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.