Kuroyuki Hime

Noal left his country when he was young, and now when he hears that it's invaded by occupation forces, he rushed to join the oppressor's side. Eight years have passed since occupation, but resistance is still breathing. Noal nicknamed as "Black Angel" is in the avant-guard of resistance submission. One day mysterious woman Sariel shows up before him and asks if he wants to become the king of this country. These words resonate in his mind, and his heart starts to change.

[From vndbreview]