[He knows that Merlin and probably others are trapped inside the mirrors, but he sees nobody besides the all-encompassing shadow in this one, so surely it can be expended. He marches up to Darin and, unless stopped, rams his sword into the glass tip-first next to him.]

That thing may be part of you, but it isn't all that you are, and if it tries to take over the Darin I know, then I'll help wrestle it back down. Everything's got a weakness. Everything! Even an Archfiend. We'll figure out what that is, and then the bastard will quake with fear.

[He really is determined, and he hopes that he can invigorate Darin a little if nothing else. He seems more resigned than anything else, and it's hardly any wonder, given what he has on his shoulders. Hijikata isn't quite as good at intense pep-talks as Gintoki back home, but he's doing his best!]