Shinkon Quest

Shinkon Quest summary:

Harold is the descendant of the hero who defeated the evil demon king. In this peaceful era, Harold has become a convenient handyman for the townsfolk.
One day, a sacred book predicting the world's destruction is discovered. The condition to avert this catastrophe is... "you must complete the 'Newlyweds Quest' with the demon king's daughter." Thus begins Harold's unexpected married life with Yona, the demon king's daughter.
While Harold still feels bewildered by all this, not only can Yona perfectly handle the household chores, she sweetly pampers him when he's tired. However, she harbors a secret...