The Seirei Realm is a realm in between Soul Society and the Living realm. It was created by the onigami durign the rebellion in hopes of getting souls into their territory instead, hoping to fuel their Empire. The realm has been inaccessible since it was invaded by the Teisuke controlled Underground, when they purge the Onigami.
Seirei realm is mainly a large town modeled after feudal era Kyoto,japan, the rest of the vast seemingly endless realm is made of mountain ranges and dense forests. The only inhabited part of the seirei realm being the town filled with nothing but spirits.
The seirei realm is inhabited by nothing but souls and occasionally are visited by humans and always watched by onigami. The souls live happy lives close to there families and loved ones, while living a happy after life safe and care free in the seirei realm. Most soul work as farmers or merchants, others waiters/waitresses or even a few are lumberjacks.
The Soul who live and work inside the seirei realm pay a land and living tax all in one payment to the onigami empire in a monthly sum of cash. All but a small few mind this payments since the onigami don't ask much and do help them when needed. Also the fact that they are living in a place no hollow can enter.
The portals to and from the Seirei realm are protected by a mysterious barrier that stops hollows from entering the realm unless a portal is open from the inside straight to hueco mundo.
There are a numerous amount of portal in the human world that lead to the seirei realm with instant accsess. All the portals seem to have a habit of being in random places only being able to be seen and used by spirit sensitive and souls they appear as trashcans, brickwalls, trees and suck random things around karakura town.As there are numerous portals to the seirei realm they all lead to one spot, the front base of the seirei realm town, a large wooden gate stats there 10 by 10 feet. That gate leads back to the living realm throwing the person out at a random area of a portal.
There is another gate much large on the west side of the town standing 20 by 20 feet. That gate is the portal to Befri Eindom, the onigami's home realm.Normally 6 onigami guard the gates and allow free travel.