[@Double] Hey! This is a pretty neat idea, but a few notes. 

Firstly, the Rebellion has existed for three days. It only pulled itself together in the aftermath of the temples notifying the world the Avatar was in fact alive. 

Two, like I said, really cool concept; however, this guy doesn't really have any need to join the rebellion. Honestly, his status quo stays the same regardless of how the war - his character sheet says he detests the Earth Kingdom, sure, but is that really enough to put himself at risk that joining the Rebellion would do?

Three, I like the mystery of his identity but I just want to make sure you've larrady planned put his appearance for when the mask comes off!