Ahh...

Here is where some of your major weaknesses are showing through.
I can tell you need a lot of practice in anatomy
Even for a manga/anime styled piece. The eyes are very large, and misshapen. They are also two different sizes. But it is the eye on the left side that should be smaller.
The chin seems to be sinking in to the neck as if he has his head tilted down and has pulled his head back as far as his body will let it go. From there you move to a poor connection of the neck to the torso. It should flow in to the clavicle. Also don't forget there are muscles leading from the shoulders to the neck and then in to the back of the neck. And lets not forget your shoulders. They should be wider. At the moment you have this disproportionate head setting on this scrawny body.

Now on to the costume. When working with blacks and dark colors you need to make good use of highlights and some color theory. using dark blues and purples enhancement the over all appeal of the black coat is not uncommon and will add some serious appeal to the costume.