Thank you for your nice comment! (Ooh, someone is calling it perfect ) Well, actually it's just a black ink pencil, one of those with a sort of liquid ink which leaves a big sort of blotch if you leave it against the paper too long. It's kind of hard to use when doing details such as eyes, (which you probably can see if you look closely) but if you are careful, it should look pretty good in the end.
Black ink pencil? I guess I'll give it a try. As soon as I acquire one, anyway... Usually I used my fountain pen or quill, but it's nearly impossible to paint larger areas smoothly with my thin writing nibs. Oh, well.
Anyway, I wait for even more Kuro-related fanart. It's almost sad how addicted I am to the thing.