I presume you're talking about Corrupt Chi - there's generally two main ways you can get it... it gets offered to you (via the Wulin Sage) by a Demon in a moment of great extremis (A Critical Failure), and your character chooses it, OR your character gets unlucky in discovering a Kung Fu Book of Knowledge and you learn it... and it turns out to be a corrupt technique and gives you Demon Chi.
Then there's Void Chi - which is very powerful but very bad for well, everybody else.
Once you've read a bit more of the book and have the basics of the system in your head, turn to page 367, where all the bits of Demon and Void Chi are explained.
I also think becoming a baneful human works like that (essentially you turning your back on all aspects of the divine view of the world, including demons; you become a phenomenally powerful warrior who learns at a superhuman pace, but everybody is afraid of you). But my memory may be tricking me.