Reisen's motive is to somehow save the princess in his fight. So of course he needs the demon king alive for that. So he'll kill anyone
That was a pretty obvious death for Reisen. He didn't even end up fighting that chef with a sneak attack! But his loss also shows just how strong Yakuto is.
Yakuto's motive for killing the demon lord, because he thinks the demon lord has changed things, is pretty interesting. I like that he didn't care if other people called him out about how simple that seemed though. He's really thought things through and will keep with that motive. But Mikoto's suspecting he actually has something else planned in the future.
Seems Chakko, Hanni, Mikoto, and Freyr are ok with Yakuto's plan. Reisen's been forced into it because he's now a zombie, Hien's gonna be passive, and now we have a new classmate who seems interested in them. I wonder how having Professor Maxwell at their side will change things?