Flesh it out.
It has its strengths and its faults. I love the artistry - it's both vivid and dark. However, the movie felt very slow paced, especially in places where it should have been exactly the opposite. This is especially noticeable when the demon is rushing towards the protagonist. The animation is somewhat sparse, giving it more of a slideshow or comic feel than a movie. That's fine, but just be sure of what you're aiming for. Finally (don't worry, I did like it), be sure to flesh out a more distinct story. There's a lot of demon-fighting/dark-tormented-hero here on NG and elsewheres. If you don't give specifics and depth, you run the risk of making this a rather pretty but generic animation. All that said, nice work!