Castle of the Zodiac

Every person in the world at least knows or heard of the zodiac. The great gods of the sky some people say. Yet little do they know these Zodiacs were once people who had been living the same everyday life they had. They were called the Zodiac Guardians as in "ones who protect the zodiac"
What do they protect exactly? No one knows, No one but the twelve young children who are about to become to guardians themselves. Why were they chosen? What's even more confusing is why they were chosen over during the end of another 2,000th year in the world.