Imperial Possession

It is a documented fact, reported by several Emperors, that the Ilkani Emperor has access to all the memories of every previous Emperor by way of the Heart of Ilkana. In discussing it, the Emperors have described it a bit like having a Privy Council in their head. It might not be unexpected then that when an individual ascends the throne their demeanor changes. They often become much more thoughtful, formal, and reticient. The younger they are when they take up the Heart, the more dramatic the change.
This was most clearly observed in the case of child-Emperor Hylorian, who swiftly became a studious, well-spoken young man when previously he had a reputation as a wild child. This lead to rumors that the Emperor had been possessed by one of his predecessors. This conspiracy theory comes and goes based on how competent and strong-willed the individual Emperor is seen as being. When an Emperor is perceived as being iron-willed and unmanipulable, invariably this conspiracy theory starts resurfacing.
While this is very clearly used as a political weapon, there is a certain portion of the Empire that believes that this actually can happen. To allay the public, the 110th Emperor allowed herself to be examined by a team of experts in mental coercion selected by the Hierarchy to verify that they were free of possession or other mental manipulation. This was established as Imperial tradition by the 130th Emperor, occurring on a decennial basis on the date of the Imperial Jubilee. This has a twofold purpose, one to ensure that the Emperor is their own person, it also serves as a public demonstration of Imperial submission to the will of the Houses as a whole.
The existence is rumor has lead to an entire field of study doing deep study of the personality and actions to try to deduce symptoms of possession.