Tomofuji Yuu Manga

Saliphie, the 99th sacrifice to the terrifying demon king, learns two secrets about the king: The first, that he has been letting the sacrifices go in secret. The second, that half of his blood is that of a human. She gets to know the king's kindness and sorrow, and then it's announced that the king has taken Saliphie, who wishes to become a source of energy for the king, as his queen, and...?