I like it very much, but maybe more of a frown and lowered outer edges of the brows would convey more fatigue. The expression right now just seems a bit too tense to me. The body language is right but I'm seeing hard concentration in the face.
EDIT: Maybe Droop the shoulders a bit as well and a little forward slump in the upper chest too.
EDIT 2: Great lighting...
[ Edited: 07 September 2013 08:01 PM by Jaderail ]
all that Jaderail said, plus (imo) less colorful/saturated light would possibly help: the warm fireplace light (i guess it's a fireplace that's giving light to your scene) makes it cozy; so a colder light could possibly make it look more lonely and not contrast with the feelings you are wanting to make stand out.
Yellowish lights can look more 'depressing' than orange and red, so it might be worth a try with a less red dominant light color (without going into yellow-green tints, that would make it look spectral).
I am testing a different camera angle. Have changed the pose and played with the lighting.
Comments are appreciated.
I do like this angle much better, now remember this. Most places have some Ambient light (fill light) not many places in the world are 100% dark just because it is night. Even setting in my room at midnight with the lights off I can see my room somewhat. Lights from my windows cast from street lights across the road, a Full moon will really add light. To get good renders think in real world terms. Heck even test it some time for yourself. Turn off your lights with your eyes closed for a few seconds then open them. Now look around, you will be surprised just how much you can see.
I darkened Satsuki's feet a bit, to blend her in the environment (and to fit in better with the dark ground around the mutant's feet area), and let her face stand out better.
This is looking very good. To me the only thing that detracts from the image is the Hair color. I think it would look much better with a real world hair color rather than a she is a rebel type hair color.