Gachi Koi Maou-Sama

Gachi Koi Maou-Sama summary:

A hero undertakes the task of defeating the Demon King for the sake of world peace. When he arrives at the Demon King's castle, he is greeted by the Demon King with a marriage certificate in his hand! The hero is bewildered by the Demon King's strong appeal to marry him, but...? A love comedy about a hard-loving Demon King and a salt-addicted hero whose world is in danger of extinction!