I wonder if Yuuki knows how to extract the demon heart out of a person. Because that's needed to save Io. Nobody ever dies in this story, no matter how much the villains talk about killing people, so there's no other choice.
I'm kinda just mad how the MC have not actually trained the limits of his power, sure he wants a peaceful life but surely he could have at least caught on the fact that he's bound to encounter this after diving into this side of his reality..