The differences in difficulty are in how the shading/form is for each character you're trying to draw (this may not be with you, but its how it is with me lol). I think It may be that way for you because of who you're trying to draw (krystal/lucario) need much more detail than your standard anime character (kagome in this case).
Another reason is if you break down the basic shapes of anime, its like oval head, curved square large eyes, and a side triangle with no base for the nose. The main body, when broken down to its most basic shape, is just a curved triangle (sorry guys, I dont know the words for art, If I can draw it, I do)
What Im trying to get at here, Is that people in games usually have to be done in alot more detail, might even be that you have to transfer a 3D character to a 2D form, I always find trouble doing that.
I have no clue if any of you will understand this, I just got off work and Im not thinking at 110% right now lol....