The emperor of Xing is the father of both Ling Yao and Mei Chang as well as forty-one other royal scions.
As Emperor, he is sent a concubine from each of the fifty families that make up the nation in order to bear a child. He is rumored to be of failing health, prompting both Ling and May to venture to Amestris in order to find the secret to immortality so as to raise the standing of their respective clans. Throughout the story, May Chang reveals that Her father is a very heartless and greedy man, as after she finds out that the Philosopher's Stone is made using human souls she is certain that he would have no qualms murdering any number of citizens to create one.
By 1917, the current emperor seems to have either died or retired, leaving the imperial throne to his 12th son Ling, presumably due to Ling's acquisition of a Philosopher's Stone.