So if im not mistaken Herriman has normal human reaction times, granted they may be peak, but theyre normal. No normal human man could react to that at fifteen feet Mifune is moving faster than a bullet and your guy not only sees him but has enough time to both recognize his attack, mutate his arm and throw it to the side, and point a sword at him. Realistically by the time Herriman got his arm to the side he would be stabbed he isn't fast enough to move like that, and the fact he mutated first which im guessing isn't instantaneous based on the cracking and such is equally impossible.