The Emperor and the Imperial Court
Ultimate rule of the Empire belongs to the Emperor, Bearer of the Undying Flame of Heaven although in practice the Emperor is little more than a ceremonial role. The position is not hereditary; instead when an Emperor dies his successor is determined by the Emperor's own priesthood.
The Undying Flame of Heaven is a divine portion of the Emperor's soul, part of the Imperial Flame that is reborn in successive Emperors. The role of the Emperor's priesthood is to use divination to find the person whom the Undying Flame passes to upon the Emperor's death. This is commonly a newborn child, but adult candidates are not unknown. The priesthood claim that the Undying Flame knows the most suitable candidate for the job, and will move according to the needs of the Empire.
The Emperor is raised and trained by the priesthood, and whilst he bears the Undying Flame his family are revered and looked after in Reflected Glory, the Emperor's palace complex. The families of former Emperors tend to remain in Reflected Glory as courtiers and hangers-on.
Although the priesthood would appear to have considerable powers as "kingmakers", in reality the duties of the Emperor are mostly ceremonial. The Emperor is considered the link between the mortal world and the Ten Thousand Immortals, and it his duty to the Empire to travel almost constantly between sacred sites, there to meet with and appease the Immortals. Practical matters and the day to day running of the Empire are left almost entirely to the bureaucracy.