So I realized something that a lot of you probably didn't notice but I found after browsing through the wiki.
The heart you receive from The Outsider is the Empresses, or at least possesses the soul of the Empress.
Hints at this:
The most obvious, the voice actress is the same as the voice of the Empress.
Granny Rags says "Nothing's been the same since her death! Poor child! Her spirit lives on – trapped – misused – and for what purpose?"
When used on Sokolov: "Anton Sokolov. He knew me once. And did much to set me on my path."
Finally, on Daud: "Why have you brought me here? Am I to forgive this man for what he did?"
As far as I'm concerned this is solid evidence. Sorry if you all already realized this but it kind of blew my mind as I wasn't paying a lot of attention at the beginning of the game.
I put contains spoilers in the thread title.. TWICE! So don't bitch.