Chapter 299: The Reality Of Mazuru’s Zanpakuto
The Ōken!
It was not the first time Grimmjow had heard this term.
As one of the Espadas, he also knew at least a part about Aizen's purpose.
The reason for the decisive battle between Aizen and the Soul Society was that he wanted to use the Karakura Town of the world of living, which was a Jūreichi (Concentrated Spirit Zone), to create the Ōken.
Although he doesn't know what the Ōken is, it could be seen that this thing was something important from the fact that Aizen wanted to create this thing, and the shinigami were fighting him to stop him from obtaining it.
As for Sojiro, he had never heard of Ōken before. After all, he had never even heard of Zero Division, so it would naturally be difficult for him to know about Ōken.
However, according to Mazuru's statement, creating the Ōken seemed to require a lot of souls.
Sojiro didn't know that creating the Ōken not only needed souls, but also a Jūreichi.
There were conditions that needed to be met in order to create the Ōken – hundred thousand souls and a Jūreichi with a radius of one spiritual ri (usually about one third of an English mile and now has a standardized length of a half-kilometer (500 meters or 1,640 feet or 0.311 miles)).
The so-called Jūreichi refers to the point in the Human World that possesses the greatest concentration of spiritual beings. That place would move with the times, and Karakura Town, which was referred to as District 3600 by the shinigami, was situated on the current Jūreichi.
This was why the Soul Society determined Karakura Town as the location of the decisive battle and moved it after confirming Aizen's purpose.