I dunno, guys. It feels like everyone is being played.
Lapience, for example, is showing the sort of anger and hatred that has a specific cause - some kind of trauma she suffered in the past that makes her hate and despise humans.
She is powerful enough that she doesn't need to be subtle in order to get what she wants. She can just go off on her own and murder humans to her heart's content.
And yet, the Demon King is somehow able to keep her more-or-less in-check. And I don't just mean the whole thing where she can kill Lapience and resurrect her over and over again. There's something going on there that's keeping Lapience from going off into the deep-end.
I don't know about the others. Sure, Maria comes of as being kinda twisted, but I don't get the sense of her being some kind of puppet master. And the other two... One has already said that they're bored of it, and the other strikes me as a musclehead who only has fighting, food, and maybe sex on her brain.
It's got to be someone else - someone who benefits from exterminating humans from the world, or at the very least perpetuating the conflict.
In the first chapter, there was a council of the remaining rulers/high-ups among the human nations deciding what to do--where the initial "marry a human to the Demon King" plan was hatched.
There, we see various (unnamed) individuals arguing over whether to continue fighting, or seek to parley. And a supposed king--drunk and mad that the last bottle had just been emptied--said that even
if the demons agreed to a truce, "all the funding for our armies and general manpower would go to waste." (ch.1p.13).
That right there tells me that even among the humans who are being pushed to the brink of extinction, they fat cats and rulers are worried about their coffers and spent wealth. Not the existential threat that is all of them ending up in pieces the next day--but their pocketbooks and gold vaults.
Personal greed and ambition will make some people do anything. I would actually bet that it's a plot with numerous actors, both human and demon (and potentially otherworldly, even) that are behind the war in general, and the Demon King is being controlled as a part of that.
Plus, the opening narration describes the Demon King and Generals showing up out of nowhere and immediately wiping half the human nations off the map, after all--that's a
lot of seeming coordination right on day one, with no mention of them being a factor or even known beforehand (thought maybe that will come up later, and the history of the realm just hasn't been conveyed at this time).
But you are correct - Lapience
is very violent and trigger-happy, but is seemingly wholly constrained by Milfina in ways that can't be explained by mere "fear of corporeal punishment". I would imagine it's a deep, abiding love; she's
very upset at Cecilia showing up and being wed to her Demon King, which sorta sounds like "don't you dare encroach on what's
mine", potentially. And the others seem....well, rather at ease being idle about the castle, at least when we meet them. Cecilia might be there as part of a ceasefire, but I would expect they'd be up to something involving the war effort, though we've just not seen enough to say that they're actually just lazing around in a suspicious way.
I think the demon generals are all fakeouts, but that the actual hands behind the curtain are many.
The specifics are too broad at present with what little we've been given, but we know that humans possess magic and some even possess unique skills--like Cecilia's eyes. So the potential is certainly there, for humans to be involved in this plot.