Please check out my book if you get a chance! (I am the author!) It even has a sequel already!

In the Three Lands, Angels and Demons can inhabit human hosts, should the host accept them. Angels are revered, while Demons are killed onsite. So when the Angel Aturah the Wise asks to travel with one of the last remaining magic users in the Three Lands, Grammard Poske can’t refuse. Soon into their journey, Grammard is abducted by a group of Demons. His only way to survive is to summon the Demon Paos into him. While Grammard and Paos battle over control of their shared body, Grammard discovers a plot for Demons to rule the world that has been in progress for over a century.

Available on Amazon.com: http://www.amazon.com/Dominating-Demon- ... mon+within