I like the character and this is looking very cool but the animation needs some work. DO THIS; stand up and make the most exaggerated ridiculous possible breathing motion you can, pretend you've just sprinted up a mountain. What does the motion look like? Take that motion and dial it back. For me the basic movement is bend down at the knees, drop the shoulders -> extend legs, pull shoulders up. Also throw in a bit of hand and head motion and the obvious chest expansion. You've hit most of those marks but the legs don't bend properly and the hand motion is odd. I would also suggest while doing this to observe the order in which your body moves, everything doesn't happen at once, your shoulders hit their peak after your chest does. This is referred to as "follow through and overlapping action."
Often it's a good idea to try these things out to realise what the mechanics of the body are then you can go ahead and tone it up or down depending on what you're going for. Another small note but her uh, thing she's wearing instead of pants, should not move like that, it implies that her hips are compressing which is physically impossible. The only reason to even touch that area is if she's bending her leg from the hip. Also consider that when we bend our knees our whole body moves, you need to think of the body like a series of levers, if I want to move my knee down then my upper and lower legs have to become diagonal. Bones can't squish, they can only rotate.
Don't forget to act it out, I guarantee you'll learn something. Good luck
