Board Thread:Questions and Answers/@comment-24317446-20150327015210

Why is Aizen classified as a Soul? By definition, a Soul is any one of these:

- Pluses - benign ghosts in the Human World.

- Jibakurei - a spirit who is not able to leave the Human World that easily because he or she regrets leaving something behind.

- Tsukirei - a spirit very similar to a Jibakurei as it is also unable to leave the Human World because of something he or she regrets leaving behind.

- Hollow - a Plus which has lost their heart and become a being of pure instinct.

- Arrancar - a Hollow that has removed its mask, thus gaining Shinigami-like powers and taking on a more humanoid form.

- Shinigami - a spiritual being that is responsible for regulating the balance of Souls between the Human World and Soul Society.

It's fairly clear that Aizen is not any of these. He makes it abundantly clear throughout his conversations that he has transcended both Shinigami and Hollows. Transcendence, by definition, is existence or experience beyond the normal or physical level. Basically, he, along with Isshin, suggests several times that he exists outside of the dimensions of both Shinigami and Hollows, and by extension, all of the other classifications of a Soul. Also, his fusion, or 'subjugation', of the Hogyoku has completely altered his spiritual physiology, granting him several different forms, immortality, and abilities such as teleportation and Kyoka Suigetsu itself absorbed into him. He has been transformed to such an extent by the Hogyoku that I don't think it is even accurate to classify him a Soul anymore.

I think it would be much more accurate to classify him as a God, and here's why. Chapter 617 - Return of the God is clearly referring to Aizen, as this is the point that he is fully reintroduced into the story, along with his presentation on the cover. Why would Kubo refer to him as a God, if he was not one? If not a God, then he certainly isn't a Soul. I suppose, however, that raises the question of if there is any dimensions of existence between Soul and God, and if so, does Aizen exist in these dimensions?

As a side note, Aizen's profession is not a Shinigami, as a profession is a paid occupation, especially one that involves prolonged training and a formal qualification. Since Aizen is technically a prisoner, he would have no occupation. 