See, this is an example of the misleading nature of your terminology -- specifically, "ground." (I don't mean you personally, but the conceptual image is disconnected from the reality.)
Mifune can in no way be using "ground" when he is literally disconnected from it. It is not just gravity, either. He is plainly using active control of his momentum and the moment of his body, in one case curling the leg under to allow a counter-moment on the top of the throw, and in another arcing his legs actively back and up to increase counter moment in the throw, and create shear at the connection.
Misleading? Not really, at least not to anyone that can actually do this stuff Erick.
But then again I don't know anyone that's met you and vouched that you can do any of these things anyways
Maybe you can come up with a step by step instructional vid explaining in your own terms of momentum circular omega force dysfunctional vectors, how "grounds" a push on one leg, and how that skill translates into helping with throws etc