- The main character was a young boy who was possessed by some sort of demon (so, fantasy); a tree might have been related here
- The cover was this character with a toothy grin
- The title was one word starting with K
- It was a series
- I found the first in the series in [a book store](http://www.bolen.bc.ca/) somewhere between 2007 and 2011; it was the only one there at the time