Awesome. I like the simplicity and the implied action-- there aren't motion lines or anything that would crowd it up, but yet the image has interesting details like the wrinkles in the shirt, and the scabbard chain.
It's clear that you're off to a very strong start in 2013. The overall composition is simple yet succeeds in every area because all parts compliment each other and do not overpower one another. The same goes for the palette too. In addition, I love the pose of the ninja: humble, noble and full of power, honor, and courage. Spectacular job!