The Soul Reapers known as Shinigami in Japanese are spirit beings that inhabit the center of the Soul Society in the manga Bleach.
Soul Reapers travel to the world of the living to perform soul burials on spirits that have yet to find peace and pass on to the Soul Society.
Soul Reapers also have the task of destroying Hollows, evil spirits that have lost their connection to humanity.
When a Soul Reaper executes a hollow that didn't commit great crimes in life they purify the soul and return it to the Soul Society.
The only time a Soul Reaper sends a Soul or a Hollow to Hell is if that person committed great crimes while they were alive.
Since their beginning the Soul Reapers have been working to protect humans from Hollows by using their large army of Soul Reapers.
Within that army there are three main branches, the Gotei 13, the Demon Arts Division, and the Special Forces.
The Gotei 13 is the regular army and has 13 units that are led by 13 Captains.
Under each captain is a lieutenant who communicates directly between them and the lower ranks.
Each unit is different and some of these units aren't even combat capable, but instead are medical specialist.
The Demon Arts Division is made up of the Soul Reapers that are best at Demon Arts.
The Demon Arts Division is responsible for opening and closing the gates between the living world and the Soul Society.
All other activities that the Demon Arts Division carry out are strictly classified and kept to the members of the team.
The Special Forces is smaller than the Gotei 13 and respond to attacks and Hollows that are too powerful for the regular guard to handle.
All Soul Reapers carry a Zanpaku- to, a sword that has multiple forms that base themselves off of the power that the sword and the owner carry.
The basic uniform for the Soul Reapers is a black martial arts uniform that is very loose and baggy.
The Soul Reaper use black swallow tailed moths to signal when they have arrived or leave a place.
Advancement to captain's rank
The Soul Reaper's captain seats can only be filled when one of three conditions are met.
The first option for promotion is to take the promotion's exam.
To pass the exam the requires the Soul Reaper to perform their Zanpakuto's final release in the presence of the Commander General (who resides over the 1st Division) and two other existing captains.
A Soul Reaper's second option would be to get recommendations from six of the thirteen captains and at approval from three of the remaining captains.
The final choice for a Soul Reaper is to slay the captain that hold the seat that they want.
Lieutenant seats and below.
The Lieutenant seat is held by the Division's second most powerful Soul Reaper and is usually chosen by the Division's Captain.
Any seat beneath the Lieutenant is based on any factor from strength, ability, and experience. These seats can also be held by multiple people at one time, as is seen in the 13th Division.
The Captains during the Soul Society arc.
1st divisions captain is the oldest and singularly most powerful of the Soul Reapers, Shigekuni Yamamoto- Genryusai.
2nd Division captain is Yoruichi Shihouin's former pupil Soifon.
3rd division is led by the deceptive Gin Ichimaru.
4th division is headed by the medical captain Retsu Unohana.
5th division has the traitorous Sosuke Aizen at it's command.
6th Division falls in the capable hands of Byakuya Kuchiki.
7th Division's captain is the helmeted Sajin Komamura.
8th Division captain is the laid back and womanizing Shunsui Kyoraku.
9th Division was led by the blind Soul Reaper Kaname Tosen.
10th Division has the youngest captain Toshiro Hitsugaya leading.
11th Division has the blood thirsty Kenpachi Zaraki leading it's men into battle.
12th Division was once led by Kisuke Urahara but now falls under the demented Mayuri Kurotsuchi.
13th Division belongs to the ill yet revered Jushiro Ukitake.
Replacements after the Soul Society Arc.
No one has been named as the new captains to replace the 3rd, 5th, and 9th division captains vacant seats. It would be logical for their lieutenants to take their seats, but they would first have to pass the promotions test.
Lieutenant's by Division
1st Division- Chojiro Sasakiba
2nd Division - Marechiyo Omaeda
3rd - Izuru Kira
4th - Isane Kotetsu
5th - Momo Hinamori
6th - Renji Abarai
7th - Tetsuzaemon Iba
8th - Nanao Ise
9th - Shuhei Hisagi
10th - Rangiku Matsumoto
11th - Yachiru Kusajishi
12th - Nemu Kurotsuchi
13th - Kaien Shiba (deceased)