Ken to Mahou no Zeikin Taisaku @comic

In a world governed by a peculiar law, a hero and a demon king join hands, causing an angel to appear. The angel announces that the hero has received half the world as a gift, but it is subject to a tax. This law is revealed to be a divine tax. Frustrated by the high tax on such a vast gift, a man devises a plan to avoid paying it. He enters a fake marriage with the demon king and enlists the help of a girl. The girl is a survivor of the Zeirishi, a rare occupation capable of rivaling tax angels.