- The main character was a young (probably 10–15 years old) boy who was possessed by some sort of demon (so, fantasy); a tree might have been related here
- This might have caused him to (want to?) eat people
- Said possession happens during the course of the book, and the character is still himself, only more… evil
- The cover was this character with a sharp-toothed grin
- The title was one word starting with K
- It was a series
- I found the first in the series in a book store somewhere between 2007 and 2011; it was the only one there at the time
This is a bit of a stretch and it’s been so long that I’m not completely sure of any of the details. Still, if anything can be found from it…