I'm starting to believe that the protagonist's got enough depth it was never an issue of the other girls failing to take the initiative, but of being fundamentally unable to get past his armor with their shallow friendliness, and would have all been flat out rejected if they tried a confession.
That's just your usual narouslop logic: protagonist does something perfectly reasonable or called upon by the circumstances within their POV, then everyone around him is amazed at the success of his genius/crazy idea. We see other examples of this much earlier in the story like his insistence on...
Yota had said that he lost against Kinjo when he taunted him at the tournament after kidnapping his mom and Nishina, so I guess we're going the unreliable narrator route.
Demons respawn but the Demon King is an actual toddler, most likely a reference to how the archetypal DQ Hero would respawn back at the human King if he fell in battle.
It's not like the demons are guiltless in their methods, particularly because they do have some leeway with their lives and...