Invasion of Soul Society

The Invasion of Soul Society was a major conflict detailing Sōsuke Aizen's and Gin Ichimaru's attack on the Real Karakura Town located in Soul Society, and the final battle between Ichigo Kurosaki and Sōsuke Aizen

The conflict started when Aizen and Gin arrived in Soul Society where the Real Karakura Town was located and started to chase down Ichigo's classmates, Keigo Asano and Tatsuki Arisawa

The conflict ended when Ichigo arrived after having learned the Final Getsuga Tenshō to confront Aizen in a final battle and defeat him. Aizen was then sealed by Kisuke Urahara and Ichigo lost his Shinigami powers due to the use of the Final Getsuga Tenshō.

Prelude
Having defeated their challengers in the fake Karakura Town, Sōsuke Aizen and Gin Ichimaru head through the Dangai Precipice World in order to reach the real Karakura Town in Soul Society. Soon however, they are confronted by the Kōtotsu and Gin warns Aizen to hurry up as they can do nothing to stop it. Aizen however, walks up to it and allows it to collide with him, leaving himself unharmed and the Kōtotsu destroyed. Aizen then invites Gin to carry on with him towards the Soul Society

Back in the fake Karakura town, Isshin Kurosaki hobbles towards his son and headbutts him to pull him out of his state of awe. Ichigo says that their situation is hopeless as they cannot defeat Aizen with that amount of Reiatsu. Isshin realizes that Ichigo is able to sense Aizen's Reiatsu and tells him to come with him as if he does not, all of Karakura Town will be destroyed and his friends will die. Ichigo regains his resolve and the two head open a Senkaimon.

Meanwhile, in Soul Society, Aizen notes that they did not end up at Karakura Town but rather a little ways away from it. Gin asks Aizen not to make it sound like it was his fault as it was Aizen's destroying of the Kōtotsu that made them land here. Aizen admits that it is true and the two walk towards Karakura Town.

In the Dangai, Isshin and Ichigo run towards Soul Society when Isshin stops and notes that he cannot sense the Kōtotsu. Isshin says that this gives him an opportunity to have Ichigo learn the Final Getsuga Tensho. Isshin explains that the Dangai is cut off from time and space and that time flows faster here. This means spending considerable time in here will result in little time passing outside. Isshin explains to Ichigo that he will stop the current as Ichigo enters Jinzen.