His identity destined him to be subordinate to others for the rest of his life.
He must hide his own sun-like brilliance and depend on another sun all his life, just because that person is a legitimate son and he is a concubine.
He was loyal and died in order to protect that person's empire. Before he died, he witnessed that person's betrayal. The resentment in his heart caused his soul to travel through time and space to avoid reincarnation. This time, he wants to tell everyone that he is the sun and his name is Yao.