well his head and torso stays still, just try this movement out yourself, see how your body moves.
I made a quick atempt to show you how I would approach this, I think if theres going to be a step it would be to step back with a simple swing like this but there should be more focus on the shoulders because your character tends to hit whilst walking also, a full step into a swing would involve much more behind the sword (whatever weapon) and possibly a hard step forward to exagerate the force.

small step

larger step
of course there should be much more attention to time spacing, to make it as readable as possible. Plus maybe he shouldn't step atall.
well hope this helps neway. goodluck