The Demon King's Wife?!

The hero defeating the demon king and bringing peace to the land. Such a cliche story that it is used quite prevalently. But must it be this way? What if there were a more peaceful means of resolving such conflict. What if the two sides could join together in peace? With there being no need for either the hero or demon king to die. The main problem is there is no cultural diffusion between these two groups. Seeing this question the demon king vows to end this conflict peacefully. Though at what cost for our hero?  (Art by: Tiger Ki)