Mutsuki really didn't do anything tbh, just threw a couple knives. We've seen enough of Saiko to know that she crushes. She one-shot Nutcracker.
To be fair, you remember that first time, he couldn't do anything and acknowledge that he has to get better and not just be a person to open the spot for "fighters" to attack. So instead struggle, he pretty much got Torso guy cornered. Now, his new test is to fight a ghoul that fights fire with fire.
Saiko is proven that she can be really strong; however, she needs someone to open that gap. Now, alone, she has to experience it. Will it be now? Don't know.