Let’s follow the train of thought this king has for a moment, because I find it hilarious.
Demons are getting together and might pose a threat because that’s what happens when an oppressed group suddenly becomes significantly more powerful->kidnap random girl to experiment on her-> experiments work perfectly-> don’t put her out on the field, instead do more experiments on willing participants -> the only surviving participant is the brother of the girl you just kidnapped like a year ago -> send out the brother instead of restraining him and investigating why it works on only this family, or at the very least trying to figure it out subtly -> send him on a suicide mission -> he comes back alive, so you send him on increasingly dangerous suicide missions -> when he survives every single suicide mission you bring him into your capital city, have him sit within arms reach of you, and then show him that you kidnapped his sister and did experiments on her so he has an actual motive to attack you
Simply genius level planning from our king. Genuinely stunned that he had the foresight to try and drag the hero’s name through the mud before he executed the hero