Maou no Musume wa Yuusha to Seiryaku Kekkon Shitai

The war between Idéal, the country of demon race, and Étoile Kingdom, the country of the human races, had been going on for a long time until a peace overture was offered by the demon lord.
Following this, the demonic princess, Lieselotte, was married to the Hero, Schmerz and she'll live in the human world as a hostage of sorts.
However, this is just Lieselotte's first step toward her ambition, and her future will be full of hardship that she must overcome...