It does not feel good that the punch connected. They may have argued in the past, and maybe scuffled on the rare occasion, but not genuinely fought. Not like this, not untransformed, not... seriously. And Nitou seems to be taking it seriously. He can't make himself follow through on the attack. "C'mon... this isn't funny, mayo. Stop it." He laughs, then, because you have to laugh at a joke. Because this has to be a joke. Isn't it?

He can hear more footsteps closing in on them, and he realizes that joke or not, he can't stay. So he's diving for his sword and then preparing to make the fastest retreat that he can manage.