Naruto Chapter 460

[poopdeville]

I think that "thing" growing inside Sasuke is his "true self", like Itachi's:

http://www.onemanga.com/Naruto/386/09/
http://www.onemanga.com/Naruto/386/13/
http://www.onemanga.com/Naruto/386/14/
http://www.onemanga.com/Naruto/386/15/
http://www.onemanga.com/Naruto/386/16/

So I basically agree that it is a manifestation/personification of Sasuke's chakra and hatred.

Didn't they say that the bijuu come from places where hatred stews? I'm not saying Itachi's or Sasuke's "true self" is a bijuu. But I think that if a person has enough hatred, and enough strength and chakra dedicated to that hatred, that chakra can take on a life of its own and become a bijuu.

[Archangel]

That was just a genjutsu by Itachi, now why would Kishi make the readers see a genjutsu the characters cannot?