I think, the Devine Doctor patient is the "Beast Domain" itself he is trying to fix the flow of the Domain so that it wont affect or wipe out the human civilization. By trying to input "chaos" on its part chaos is the medicine.

my theory is, after he successfully executes the plan and corner the prince and princesses he will black mail them to gather information about the primordial seed..

Maybe he will find a way to cure the existing emperor's sickness.