黑血~Beyond Our Blood~

In an ancient land, when people do bad deeds their blood becomes darker. If someone is born with black blood, it's a symbol of evil. The main character is a member of an Empire that is already 10 years into a war and he's picked on by other kids. There's a younger prince who wants to overthrow the older prince, and the main character seems to join the army. [From Aarinfantasy Forums]