Flames

I really like the fact that these two characters are shaped by flames, it's an original idea. But I do think some lines, especially the facial lines are a little too dark. I see you've tried to add some realistic shading, but there isn't enough to match the darkness of the lines. It feels like you are trying to blend two styles (cartoony lines and realistic shading) but that it's not really working, because you're not committing enough to both. 
I think this only applies to the face though, because the clothes and hair are beautifully done and exemplify what I mean. 
I like the piece though (: