Mirio has a lot of strength which he has honed over the years. Coupled with his ability to phase through objects he is a very talented fighter. That will let him put up a good fight here, but he will still be unable to take on an opponent as fierce as Asta. Asta has tremendous levels of speed at his disposal and he can really dish out the pain. In terms of physical strength I’d likely give Asta the slight edge as well. He’ll never give up and that’s bad news for his opponents. Asta wins.