Thanks for the advices guys!
First, I gave him such big head and eyes because I'm aiming for the cartoon-cute style (...) the idle pose can be static to give more relaxed feel.
Those people were kinda right, actually. Think about it. How are you going to possibly perform the moves you listed with such a large head? Running up a wall, he'd probably fall back down with the weight of it, unless his head's full of helium (don't use that as an excuse). Maybe shrink it down from 2 to 3 heads, or just 2 and 1/2 heads if you feel that's too much. You can still achieve a cute style (I think "chibi" is the word you're going for) with small proportions, but not as small as you're doing it if you plan to have this guy animated.
A relaxed feel? That actually doesn't seem very relaxed, but rather strained, unnatural, and doesn't let much character show. Besides, how do you go from a completely relaxed position to running to walljumping in what's likely to be 2 to 3 seconds? In my opinion a tenser pose would suit this ninja well. In fact it would be closer to
the standard ninja pose. (I'm pretty sure I'm wrong when I say that's a battle stance, so you don't have to do it so dramatically.) If anything you can switch to a relaxed pose after the player has been idle for a while.
Oh by the way, that belt reads as underwear to me. Especially in 32's edit. Just saying.