First of all, I must mention that my favourite part of this image are the eyes - Sunako's gaze seems to go just behind the viewer, as if she's looking very far away. They're sharp, clean, and beautifully detailed.
There are a few areas where you may be able to improve, and the one I noticed first was her chin. The lines around her face and her features are very clean, though it seems to get a bit muddled at her chin. It's not that it is "wrong" but it seems less finished than the rest of the piece, when compared to her eyes, nose, and hair for example.
The hair itself looks like it too a considerable amount of time, and the fact you can literally see every strand is impressive. The only portion that seems to nag at me is where her hair parts on her scalp. Realistically, you should be able to see the scalp here, or have some indication that the hair comes from here. (Aside from the hair direction, like a darkening on the hairline. I can find an example, if you like.) I also know manga styles are not intended to be 100% realistic, but it may help to create more of a sense of depth.
Personally, I think this is a very strong piece that flaunts many of your artistic strengths. As with everything, there is always room to improve and I will definitely keeping watch for work from you in the future. Nicely done!