A letter Tousen wanted to write to Komamura, but couldn't. "I know that you would not only refuse this path, but destroy it." Spoilers for end of Soul Society arc.
I have often said that my path is the path of least bloodshed. It's ironic, then, that the path that leads to a world of justice is soaked with blood. I wish I could explain everything to you, why this is the path I must take, but I know that you would not only refuse this path, but destroy it. After all, your ultimate loyalty lies with the Captain-Commander and his vision of justice.
But what is his justice? In Rugonkai's outermost districts, where Shinigami rarely tread, there is no justice, no order; the strong rule, and the weak die quickly. In the living world, barely enough Shinigami patrol to even start to control the Hollows. We assign weak, low-ranked Shinigami to stop Hollows, assign only one or two to a sector where, five hundred years ago, a squad of a half-dozen would have been assigned. Then we wonder why the numbers of Hollows continue to increase, why more and more Pluses are devoured before they are found and sent to Soul Society. Even in Seireitei, which we fight to keep clean and sealed against any intrusion from outside, dozens of Shinigami die each month while off duty. They die dishonorably, from brawls or over-drinking. They are murdered, as my lady was. It happens over and over, and little, if anything, is done. There have been rumors for years that Research is using its own recruits as test subjects-- look at the mortality rates sometime-- yet no one has investigated. We Shinigami have become selfish and lazy, looking only within the four walls of Seireitei, at most, rather than out at the world that we were born to protect.
I doubt I could ever convince you that Aizen's path is the right one. At times, even I have doubts, but I do believe that almost anything would be better than what we are doing now. He plans to take over the Hollows; control them rather than fight them, and only release them if they can not be controlled. If his plan works, they will no longer attack souls in the living world arbitrarily, but instead be fed only on the souls of the wicked at a maintainable rate. Then we, the Shinigami, will be free to spread justice throughout the world, and no more innocent blood will ever be shed.
I can only hope that one day I will stand beside you in that reborn world and that, then, you will forgive me.