My proof on what "it" is *OS spoilers*

So I'm doing a slow and annotated re-read after steaming through it as fast as possible first time.

I've been reading different theories on what Xaden means at the end in his note when he says "It's yours now". I was momentarily swayed that it might be his soul however I'm swinging back unwaveringly to the fact that it's Tyrrendor.

Here's why: Chapter 6, last two pages when Xaden is processing the fact the King gave him back his title/seat in the Senarium for Tyrrendor. He's listing all the reasons he's a terrible choice for the title now that he's well, venin. And then says these:

"The only solution I can think of is you. You'll be the first to sense when I lose the rest of what makes me... Me (...) This morning showed me it's only a matter of time and reason. (...) It's not fair and you might hate me for it later, but I need you to make me a promise. Swear you'll sound the alarm if I go to far, ~that you'll keep it safe, even if it's from me."

There. That's it. This page has it all! He knows he's responsibilities and what he'll eventually become. He's not worried for he's soul, he's worried about Tyrrendor/Aretia, worried about keeping his people safe, about keeping his home protected with a plan. aka Violet, she's the plan!

Consequences of that convinces me it's Bodhi with him at the end but that I'm less sure of that.

Anyways, thanks for coming to my TedTalk, recommend going back and reading those two pages!