I think changing the background white would help on the kat&ana sprite, it is very hard to see the outline with a black background (for some reason alot of the backgrounds are black were I get my sprites)
Shading should not be hard to see. Do not be led astray by some of these comments. You can do better than this. Focus more on the outlines and the shading, because honestly, these are terrible. They can be improved, just work at it.