One In A Million

In the society, when each member is born, they get this tattoo on the back of their left ear, and they don't know it until they reach a certain age where they're put into a group of others who have the same tattoo as you. But the chances of having the same tattoo as someone is like 1 in a million so usually people just go off on their own. Meet Chelsea! She finds what her tattoo is at the certain age (16) and at the ceremony where the members are presented, she finds out that some other guy named Austin has the same one. They're forced out of the city like all the other 16 year olds to fight in a mandatory/surviving war against another society on the other side of the world. After that, if they live, they can have royalty.