Black Heart Demon [Multi-Anime love Story]

Eight kingdoms within the world-six of them are controlled by demons after a war between five of them against the demon kingdom which made all five of them lose their kingdoms. Now years later, the very last human known kingdom wishes a treaty with the demons-but there is a catch that none of them knows about, the king of the human kingdom wishes to unite the human and demon kind with a marriage between one of their kind to his only son. Will the demons allow the marriage and if so, who will marry the young prince?