Everyone in Soul Society knows of the Gotei 13 in Seireitei. Consisting of over 2600 members, and allied with the Kido Corps and the Stealth forces, it is the largest organization in soul society.
When Yamamoto-Genryūsai created the shinigami academy, his goal was partially to fill out the ranks of the gotei, to accommodate the growing needs of rapidly expanding human civilization. However, as time went on, the Gotei 13 became spread thin, all over Asia, Europe, and eventually, across the sea.
With the need for a rapid response team in critical areas, the Europe Response Agency was made, a small fifty man group stationed within Seiireitei. As humans expanded, small squads were created, a protection squad for each of the areas of human development: Africa, America, and Australia.
Eventually, the individual costs of these organizations became too much, and there was a large merger, occurring in the mid 1700’s. Gotei West was formed, tending to Europe and North America, while Gotei South (consisting of approximately 150 members) tended to Africa and South America. Gotei Australia remained, a small 20 person group, stubborn and set in their ways, making their living through bounties.
As incredible, talented shinigami began to be trained in the academy, more power was able to be diverted to the response teams that made up Gotei West and South. Gotei West soon became self sufficient as former Gotei 13 captain Menfir Kas Raizen took charge, a century and a half after the merger, in 1854. Though purview to the Central 46, Gotei West were autonomous, having strict regulations to be a response agency. In reality, they were not charged with the western world, but instead, they were an elite organization with that as its cover. Their true charge was to handle the various forbidden powers that were not to be known to soul society: Hollowfication, Quincies who become shinigami, dangerous humans, forbidden kido, artifacts, and other unspeakable acts.
Eventually, 12 individual squads, of 20 men each developed, as Gotei West rose to 240 full staff members, only twelve of which were ranked, by Gotei 13 standards, fourth seat or higher. While not as powerful as the Gotei 13, there was no doubt to the organizations effectiveness.
Unfortunately, all was not well. One member of Gotei West, a strong shinigami known as Aoken, seemed to go rouge, recently sacking the castle fortress, located far north of Seireitei, with an army of hollow he had somehow amassed. Of the 240 members of Gotei West, only seventeen (apparently) survived, the leaders of the twelve divisions, who were spared to watch their comrades die, and a lucky few who were on real world duty.
Central 46 rose to this occasion, ordering the cessation of all duties in noncritical areas. Critical response areas were assigned in New York, London, Rome, Paris, Dublin, Chicago, Las Vegas, and Istanbul, as well as three shinigami tending to Poland and Germany at all times, leaving only the strongest six members of Gotei West functional in Soul Society. Realizing they needed to respond to the rest of the world, Menfir ordered the request of new shinigami from the Gotei 13, to transfer to Gotei West, for rebuilding, and an investigation…
More recently, the gotei south, after rising to about 300 members, was utterly obliterated, leaving only one known survivor, including those on missions, who were hunted down and slaughtered. The one survivor has a forbidden zanpakuto, and remains within the Gotei West's care, in custody, his current status not known to Seireite. Meanwhile, Gotei West struggles to survive, with massive deficets in power, the majority of its building smashed, including their libraries, some of the dorms, training areas, and much more.
Without its main resources, and without backup from Central or the Gotei 13, who wish to see these 'splinter organizations' fail, Gotei West needs to find its own way to survive. Charged by central secretly to deal with forbidden powers, the survival of this organization is of the utmost importance. (See Division Information for the types). On top of a catacomb of Seikessei (the spiritual energy immune stone), a former mineshaft, prisoners posessing forbidden powers are beneith the structure. If Gotei West falls, what will become of them? And what should happen if they escape?
Beyond that, the Gotei Australia has fallen to an onslaught of demons from hell, trying to break their barriers. The true destruction of the west was when a safety precaution for its hollow generators, the secret to its power grid stemming from their infinite capacity for power, allowed the entire fortress to be overrun. Menfir trained as many of the west as he could with forbidden powers, and the handful that remain comprise the Arcana. Aoken was a fall boy for the entire event. Gotei west has withdrawn its territory, for its limited capacity, to Europe and North america alone, leaving South America, formerly taken by Gotei South to the 13 protection squads.
In addition, in order to support income for the west, Menfir has allowed the worst of the worst of ryukongai to establish a town outside the gotei west walls. Their activites in forbidden powes have risen, as they are the only ones who know of the world barrier between demons and Soul Society being bent.. and a few being loose. Their work continues, secritive, as unsuspecting recruits continue to join.
Lack of personnel, despite the strength of individuals within the gotei west, has made it impossible for the west to monitor forbidden powers AND all of the western world, not to mention the south. Negotiations melted down with the central 46, and while Menfir was allowed to keep his title, the wardship of standard hollows was re-transfered back to the patrol corps, and standard Gotei 13. Outsiders have little idea what Gotei West does anymore, but all of its efforts are now sent to demons, forbidden powers, and other unusual circumstances. [Mulder... where are the pencils?].