Shinigami

There are, to begin with, two types of shinigami-- Shinigami from Soul Society, and the Meifu shinigami. Their jobs differ in many drastic places--While Meifu shinigami exist to make sure everyone dies at their correct time, SS shinigami are given the duty to maintain the balance between the worlds. However, over time, corruption reached the head of Soul Society, and they began to distort the meaning of their duty--going so far as to start culling certain species and eventually leading to the war between the Kuinshi and the Shinigami.

The Kuinshi-Shinigami War
The Heads of SS had decided that Kuinshi, with their essence-devouring nature, posed a threat to the balance, and gave the orders to exterminate the entire species. The war lasted several long, bloody decades, during which many of the shinigami, already growing doubtful of the Center 46's totalitarian regime, began to secretly--and not so secretly--defying orders and sparing Kuinshi, in some cases even smuggling them away. The growing dissent in the ranks caused the Central 46 to withdraw the troops. In the midst of the confusion, a few hundred shinigami launched a revolution, intending to overthrow Soul Society.

The Revolution
The revolution itself barely lasted 10 years, but even in such a short time, the damage caused by the insurgents was immense. At the end of the rebellion, the rebels had lost, but had done devastating damage to the infrastructure of the Seireitei itself. The 13 surviving members of the resistance were then banished to the human realms.

The Secession
Once the resistance had been exiled, the Shinigami moved to recover and recoup from the damage they had suffered during the period of Revolution. It was during this point in time that some of the Shinigami, from Captains down to regulars, started to think about the punishment meted out to the survivors of the Resistance. Once the greatest majority of the recovery had been completed, they began to confer among themselves about their opinions on the exile and came to an unanimous decision that a sentence of permanent exile was too harsh of punishment. Thus they decided to mount a petition to Central 46 that the sentence be modified, to place a time limit upon the exile and when it came to end, allow the 13 to return to Seireitei. However, when they actually brought their petition to Central 46 publicly, they were told that it was foolish and that it would not be considered. Due to the displeasure shown, a good majority of the shinigami backing the idea of a modified sentence ceased any further attempts to press their case and went back to their stations, unquestioning the orders given to them.

There was though still a small group of shinigami that demanded that they be heard out completely and refused to be dismissed so casually. Pressing their case, the Central 46 became increasingly irate with them and after one such dismissal of their presence, a vice-captain returned their irate tirade with accusations of their corruptness and incompetence. This was the event which began the fracturing of the remaining bonds which held these few Shinigami loyal to the commands of Central 46. The verbal attack upon them was answered via a physical attack upon the vice-captain, the result of which ended in the blinding of the man's eyes. This and the following order that no one was to help the injured man proceeded to shatter the fractured loyalty beyond any possible hope of repair. Disobeying the orders, the group proceeded to not only to help the vice-captain, but also removed him and themselves from the presence of Central 46 and then outside of Seireitei entirely.

Such action drew considerable attention from more than just the governing body they had in effect severed themselves from, but also from all of those serving said body. While at first they remained a small group, with perseverance, they created for themselves a new place to live and serve out the duties they still desired to complete despite the separation from their fellow Shinigami. This successful break and resumption of their lives emboldened others of like minds whom had been too uncertain of success to act previous into leaving the ranks of Seireitei as well and joining them.

This inflamed the ire of Central 46 and orders were put into place that the upstarts were to be shut down, lethally if necessary. The first attempt failed miserably due to the readiness of those leading the new sect of Shinigami, Captains Unohana Retsu & Ukitake Jyuushirou. After the third such failure, the de'facto lead voice of Central 46 ordered that they be taken out unawares via gas introduced into their region. After some discussion on the type to be used, the order was set into motion and carried out. Unexpectedly however they survived the attack, if only due to the fact that the blind vice-captain detected the gas before it could effectively carry out its grim duty, sounded the alarm that Seireitei had sent yet another attack upon them, thus warned they managed to evacuate the area with the only casualty being the soundness of Ukitake's lungs.

It took time but finally Central 46 gave up on its attempt to destroy them, and the two co-exist with a wary caution best given when dealing with predators of equal ability. At some point within the years which followed and their numbers slowly grew to equal and then exceed that of Seireitei, they took complete control of the gates which granted access to the human realm, deciding to safe guard them from any possible future misuse.