Clive was a great dude, but unfortunately he was doomed as soon as he stepped into the a harem manga without being the MC. An elementary mistake, but occasionally you find a character who does it. He should have left as soon as he recognised Kei as a harem protagonist.
Quite interesting the ogre king demon was willing to sacrifice himself. Maybe he wasn't in perfect control of himself, as otherwise an intelligent demon should only be considering his own benefit, over anything else. I suppose there's a demon king somewhere, and both of these demons are on a mission, without a choice.