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.
But it later turns out off screen a few people where trying to kill him as result his mental state deteriorated. This was later discovered Ling Yao and he reverted back to his former self he was horrified what was happening he decided after regaining his previous mental state. By 1917, the current emperor has retired, leaving the imperial throne to his 12th son Ling, presumably due to Ling's acquisition of a Philosopher's Stone. And because he cured him from the poison he was given.