The Smiling Demon King and the □□ Hero

In countless fairy tales, the people of the continent are always happy and content. But the moment the Demon King appears, their lives become utterly miserable, even when their Divine Mage is powerful enough to be a human-shaped, self-sustaining artillery platform. Of course, that's not the point. In legends, the Demon King is always evil, cruel, and utterly inhuman. Naturally, a Demon King like that can't find a partner, so the furious, perpetually single Demon King has no choice but to kidnap a princess. As for how things end, that usually depends on the Demon King's looks. If he's burly and balding, it's doomed to be a bad ending. But if the Demon King is lucky enough to have a handsome face, congratulations to him: not only the princess, but the hero too, will be his (lol). This is an adventure story about a snarky Demon King and a lovesick hero, setting out to conquer the world (crossed out), loving and fighting each other (crossed out), and flirting with each other (crossed out). The Demon King and the hero were made for each other :-D