Not a huge manga-fan myself, but I have to admit some of these are looking real nice. Love that last one. (Saw that you just updating, I meant the one with all the paint splashes
I have one crit for the one where you were struggling with a wheat field though: That pillar is reeeeaaally distracting. If it has little or no significance to the piece, why is it more of a focus point than the character? It's blocking a beautiful view. I would move the character further to the right, and the same for the column. Lastly his foot should probably be fixed before moving on.