I really don't like how (standard) anime girls always have their back arched (to make them more cute, I guess?). It really doesn't work with a lot of movements like striking a hammer. If this pic is supposed to be epic, she needs a more dynamic pose. This just looks like some rich Instagram girl touched a hammer for the first time.
They probably have their backs arched to make their breasts more visible. I wish I was joking.
You're just like me frfr