Hmm, well i did want to save most of the reasons why they were accepted into the soul society to myself but you make
very good points. Alrighty well here you go.
SO, Basically, after the Central 46 died (A Second time, might i add) by the 'unknown force' and the spirit king and his guard fell, the Soul Society went into panic without a leader, that is, until Shunsui (Who was Acting Captain Commander) stepped up, and reigned everything together. When the 'Unknown Force' attacked Shunsui was able to get as many shinigami and spirits out of the soul society as he could (which was a surprisingly low number) at the cost of his and the other Canon Characters life's (Including Ichigo's). The Shinigami that escaped and watched as the Soul Society was torn apart and destroyed decided to follow their age old tradition of saving spirits and killing hollows. However, due to their no longer being a Seireitei they couldn't save spirits, and this served as a problem. Surprisingly Kisuke (Who had managed to survive the onslaught) managed to strike a deal with the surviving Arrancar. The Deal would be that the Arrancar would allow the Shinigami and the Pluses a place of residence until further notice, in trade Kisuke would make another Hogyoku and would give them his life afterwards in return. The Arrancar accepted this deal, and held up on their end just like Kisuke did. They received their own Hogyoku, though admittedly it was weaker than the one Aizen had, and made it for public use for any Hollows who wanted to become Arrancar, but their was a condition in doing so. Any Hollow who wanted to use the Hogyoku to become an Arrancar had to swear on their life that they would not harm any Shinigami or Pluses that resided in Hueco Mundo (I forgot the Arrancars place of residence's name other than Hueco Mundo). Of course Hollows would swear, and then they would attempt to kill Shinigami and absorb Pluses anyway, but they had found out that any Swears made in front of the Hogyoku put you into a binding contract with it, meaning if you made a swear in front of the Hogyoku and broke said swear the Hogyoku would destroy you in as painful a way as possible. Due to this Arrancar had to learn to live with Shinigami and Pluses, until eventually Shinigami and Arrancar finally broke their hatred for each-other over the course of 5 years, in which Shinigami realized that Arrancar were Hollows wanting to gain something in their life, that these Arrancar were people and had dreams, just like Shinigami, the only difference were their Spiritual Energy. This lead to an Epiphany inside of the remaining corps of the Shinigami, which changed their views on Arrancar, Quincy, Vizards, and other 'races'. However, even though Shinigami had this epiphany, they still couldn't accept normal Hollows as anything but monsters, since their un-godly hunger for spiritual energy and souls would turn them into mindless beasts, though if any Hollows showed a sign of regret for what they do than the Shinigami would help them turn into Arrancars. the Shinigami, with the help of Quincies, Arrancars, Vizards, Fullbringers, Special Humans, and any sort of hybrids, had managed to build a new Soul Society, modeled after the old one, creating new laws and replacing the old one's with upgraded ones. This took a total of another 5 years, which leads us to the present day. Due to a new Soul King not being selected however, they found no need for a new Central 46, so the person labelled as the 'strongest' of each race made a law, which stated that the Captain Commander would be in charge of everything, and could make new laws and statements so long as the Captains of the Gotei 13 and the Onmitsukaido agreed on passing the law. The only way a new Soul King would be selected and accepted would be if ALL of the captains in the Gotei 13, Commander-in-chief of the Onmitsukaido, and all of those residing in the Soul Society agreed on said person.
As for your second question, we mean just a small cut above them for you to badass your way to making him powerful and intimidating. Though, of course since your Captain-Commander you'd have +5 extra points no matter what 'race' you select. (So basically, the 5 base stats, the 20(Or however many stats points for a captain of whatever 'race' you pick) you start with, and an extra +5. Just remember that the number of your spiritual power and your stats can go above the max, as these are just for the beginning. Though you
do have to train, fight, and travel in order to get stronger, whichever you prefer mostly. I'll tell you when your Spiritual power and Stats go up in GM posts.
The Current State of the World is, to normal humans, as normal as ever. However, for Pluses and anyone with spiritual power, it's beginning to get over-run by Hollows, due to the 10 year power vacuum. Yes, the original Organizations still exist, just inside of the Soul Society, and most Shinigami don't pay attention to them unless their a Captain. Their not fairly important, though that's a matter of opinion really.
@Tensa Hiruma Yes, Sibern isn't Accessible due to the Unknown Force, though no-one knows how or why. (Yet)
@Yaoi Master Gavin Tensa is Correct, Ulqiorra was the only one to ever attain Segunda Etapa. I will allow Arrancars the ability to attain Seguna Etapa, but i won't be including it in the CS, as you can't start out with it, and have to train and fight
very hard for a chance to unlock it, but Segunda Etapa is
exetremely rare.