Shuumatsu no Harem - Fantasia

Synopsis

It's year 998, and the world has been corrupted by darkness. The next head of the small border kingdom of Nagara, Ark, has feelings for his cousin, Aurelia, but a political marriage to the Crown Prince has separated them. In order to get her back, Ark desires immense power, but a mysterious dark elf, Rati, appears in front of him. In exchange for a promise, she will give him "the power to rule the world."