Ken to Mahou no Zeikin Taisaku @comic

This world is ruled by a certain "strange law". After the hero and the demon lord decide to cooperate, a beautiful angel suddenly appeared. The angel then told the hero this: "You have obtained half of the world. A tax will be imposed related to this donation." In short, the "strange law" is paying taxes to the god! The hero, frightened by the enormous donation tax caused by their immense fortune that is "half of the world", comes up with a scheme to escape from the taxes. That is to fake a marriage with the demon lord and to rely on a certain girl.

(Source: Shogakukan, translated)