Government
The ultimate authority of shinigami are the Central 46 Chambers (中央四十六室 chūō yonjūroku shitsu). This is made up of 40 wise men and 6 judges. They are sealed into an enclave in Seireitei called seijōtōkyorin (清浄塔居林) and no one else may enter it, regardless of their military or civilian status. The decisions of the 46 Chambers are final and may not be questioned by any person, regardless of status. In addition, all decisions by the 46 Chambers are carried out, even if they require the mobilization of the shinigami army.
Army
The Gotei 13 (護廷十三隊 goteijūsantai) is arranged into 13 divisions (hence the name). Each of the divisions also has a specialization, but not all of them have been revealed yet. Notably, squad 4 is the medic/supply team, squad 11 is the battle squad (specialization in swordsmanship), and squad 12 is the research/scientific institute. Additionally, because Captain Soi Fong of the 2nd Division is the covert ops leader, it is possible that is what squad two's specialization is as well.
Ranks
As any other army, the Gotei 13 has ranks. There are 21 officer ranks, but no ranks for non-officers. The ranks and their descriptions are listed below, from highest to lowest.
Sōtaichō (総隊長, lit. General commander or Commander-General) - as the name implies, this is the Commander-General of the Gotei 13. The Commander-General is also the Captain of the 1st Division � it is implied that this is an ex officio. The current holder of this title is Shigekuni Yamamoto-Genryūsai.
Taichō(隊長, lit. unit commander) Captains are the most revered of shinigami (with the Central 46, Demon Art Corps, and Covert Ops Corps leaders possibly being on equal status). Captains are undisputably the most prominent shinigami. Every captain in Gotei 13 history has known bankai, except Kenpachi Zaraki, who won his status through sheer strength. Knowing bankai gives captains a default strength advantage of 5 to 10 times over shinigami who are not able to perform bankai. However, knowing bankai is only a fraction (although a large one) of a captain's power. They have also trained extensively, if they have not mastered, their bankai which allows them to actually use the enormous power and size of their bankai in battle. Captains are also skilled in the use of shunpo, kidou, and generally have excellent knowledge of shinigami history and battle tactics. All of these factors create a huge power-gap between captains and the next highest level; a captain can generally defeat several lieutenants at once without even needing to release his bankai.
There are three ways to become a Gotei 13 captain:
To take the captaincy proficiency test, which requires the knowledge of the final release (bankai). Presumably, this is the method through which most captains are created. The test has to be witnessed by at least three existing captains, including the Commander-General.
To be personally recommended by at least 6 captains and approved by at least 3 of the remaining 7.
To defeat the previous captain one-on-one with at least 200 witnesses from the division. Kenpachi Zaraki is thought to be the only captain who achieved his rank using this method, although this is unclear.
Fukutaichō (副隊長, lit. vice-unit commander) - this is the rank attributed to the 2nd Seat of each division. Since Captain is used to describe a unit commander, vice-captain is the most accurate translation, and is used by most fansub and scanlation groups. (The Viz translation of the manga renders the rank as the even wordier "assistant captain.") However, traditionally in real-life armies, the lieutenant has been the personal adjutant of the captain and has often been only one lieutenant per captain (as is the case for fukutaichō and taichō in Bleach). However, this does not apply to modern armies. Therefore, lieutenant is the correct real-life equivalent of this rank. Holders of this rank in Gotei 13 have also been called adjutants.
Lieutenants function as executive officers for their division and take care of day-to-day operations as well as supervise them. They (along with their captain) are not assigned to one specific squad. They generally only know shikai, but are the second strongest in their division. Some have gained bankai; this is natural seeing as they would be the most seasoned and skilled shikai users. However, these lieutenants are still not at the level of a captain for previously mentioned reasons.
Seated officers - all Gotei 13 officers who hold lower ranks than the above, are referred to seated officers. Captains have the rank of 1st Seat and lieutenants are 2nd Seat. Next to that, there are 18 more seats (3rd to 20th). 3rd seat officers are ranked higher than 4th seat, etc. There seems to be a distinction between senior and junior seated officers, just like in real-life armies. In Gotei 13, only one person can hold a senior officer rank (such as 3rd or 5th seat), but there are several holdiers of junior officer ranks (e.g. 20th seat). This may vary from division to division however, as there are two 3rd Seats in the 13th Division. In Japanese, the rank is usually spelled using the seat number followed by the word 'seat' (席 seki), e.g. (三席 sanzeki), although sometimes the word 'No.' (第, dai) is used, e.g. (第三席 daisanzeki). The seated officers of 3rd seat and below may be best compared to junior officers, especially non-commissioned ones.
