Kingdom

is a Japanese manga series by Yasuhisa Hara. The series was adapted into a anime series by Studio Pierrot that aired from June 4, 2012 to February 25, 2013. A second season was aired from June 8, 2013 to March 1, 2014.

Plot
In the Warring States Period of ancient China (475-221 BCE), Shin and Hyou are war-orphans in the kingdom of Qin. They dream of one day proving themselves on the battlefield. One day, however, Hyou is taken to the palace by a minister. Winding up on the losing side of a power-struggle, Hyou manages to return to the village, barely alive. Shin then meets a boy who closely resembles Hyou, Ei Sei. For now he is the king of Qin; later he will become the emperor Shi Huangdi.

Other Sources

 * Wikipedia (English)
 * Wikipedia (Japanese)