Um, I don't know if I missed something here, but how did Herriman miss Mifune, Dral? Mifune was off the ground (so he couldn't dodge at that moment). Mifune was moving backwards, and Herriman's swing was aimed at the center of his body (right at the spine), and he was coming from directly behind him, with the swing already halfway completed (and aimed) when he reappeared. Even if Herriman just held his axe out, Mifune's jump trajectory would have taken him back first into the blade. 

Remember, Herriman didn't just turn invisible, he phased himself out of the material world. Mifune wouldn't have heard an incoming swing, and even if he had, you usually don't hear a swing incoming until it's about halfway through and with Herriman reappearing mid-swing, there would have been no sound.