Prologue:
At the final of the winter war a tragedy happened, in the attempt to destroy Aizen Sosuke Urahara Kisuke developed a way to destroy the hougyoku. Urahara didn t realize however what the effect would be if the Hougyoku would be destroyed.
Kurosaki Ichigo was fighting a losing battle against Aizen Sosuke in a attempt to win time for Urahara his preparation to destroy the Hougyoku fused within Aizen Sosuke. Urahara finished his preparation just in time to destroy the hougyoku, the way to destroy the hougyoku when fused with a being of a high spiritual powers was surprisingly simple. In order to destroy the Hougyoku you have to in stabilize the exchange of the reiatsu between the host and the Hougyoku. Urahara didn t realize that would result in a huge spiritual explosion until it was too late. Urahara cast the spell on Aizen and the worse outcome possible happened. Aizen already having a huge amount of spiritual powers and after that adding the spiritual powers of the hougyoku resulted in a huge explosion which ripped the fabrics of space and time. Because the fake Kakaruka town was linked to Soul Society a similar explosion occurred in Soul Society, it killed every soul and shinigami residing within Soul Society which resulted in the forceful rebirth of all those souls within the real world (in the long term). The explosion in the real world had a bigger area of effect then in Soul Society, it destroyed Japan, a huge part of Asia and north America. Most of the landmass turned into a desert similar to Hueco Mundo. Only a few Shinigami survived this explosion in SS and the Human world but they all died within the next 100 years to follow, everyone in time forgot about the shinigami and the vaizards for that matter.
Humanity suffered huge amounts of casualties however due to the forceful rebirth of the souls within Soul Society this was barely noticed.
It has been nearly 350 years after the winter war and the total destruction of the shinigami and Soul Society. In the past 350 years there has been no one to take care of the dead or hollows for that matter. A variant of the Quincy rose once again under the name of: Quincy. Besides the Quincy other spiritual aware creatures came into existence, The shinigami remained to awake their powers without any guidance/education though. Vaizards were naturally born as well, arrancar were normal occurrence now too.
The reason so many spiritual aware creatures were born were the side effects of the explosion created by Urahara Kisuke. Within the closest proximity 3 shinigami with exceptional amounts of spiritual powers died (Kurosaki Ichigo, Genryusai Shigekuni Yamamoto and Aizen Sosuke), and also the hougyoku itself. The combination of these 4 huge reiatsu sources to suddenly explode made sure that even 3 and a half century later the area where they died was infused with spirit particles. However the areas began to disperse into smaller areas and over a great distance over time and created areas rich of spirit particles.
The story of this new world now begins.