Aizen had appeared. Next came Aizen's time to show off. No one could stop this dazzling performance of his. Yinsen quietly played the role of spectator, watching it all unfold firsthand.
At this point, Retsu Unohana, the captain of the Fourth Division who had learned the truth, had her lieutenant, Isane Kotetsu, use Tenkei Okura to inform the Shinigami in the Seireitei of what they had discovered, especially the captains and lieutenants.
Now the Thirteen Court Guard Squads all knew that Aizen was the one secretly stirring up trouble. Even Rukia Kuchiki's execution had been orchestrated by him. Down below, Aizen was explaining to Byakuya Kuchiki, Rukia, Renji Abarai, and Ichigo Kurosaki why he had done all this.
As a great villain, one had to have the heart of the best narrator!
A villain who did not properly explain all his schemes was not a qualified villain!
From a psychological perspective, carrying out conspiracies and plots in secret was extremely stifling and lacked an "audience." When the plan was complete and its architect felt that everything was about to end, there would be an urge to vent. It was also driven by the desire to be admired and acknowledged—I did something this incredible, so why aren't you shocked and impressed already? That was why so many villains never stopped talking at the final moment. There was scientific basis for it, really.
Even Aizen was no exception. Besides, he had been holding it in for over a century, so he needed that release even more than most villains. It was understandable that he talked a little more at a time like this!
Even as Aizen indulged in his explanation, he did not forget his real objective. He removed the Hogyoku from Rukia Kuchiki's body. Byakuya Kuchiki reacted and tried to save