Things have simply become more convenient now.
That Tier-6 Demon lurking in the capital city is none other than Vincent.
The Five Founding Dukes only began to panic then. Indeed, they possessed deep roots, but they had lived in peace for far too long, hence when they were suddenly confronted with the full-fledged assaults from the Horizon Bureau, their responses were flawed. Relying on their own strength, they managed to hold on till now, but their impending defeat has shown. Don't forget, the agreement made between their five ancestors and the Great Ancestor Emperor was that as long as they did not commit any acts of rebellion, they would be granted eternal wealth and status.
Colluding with the Demon Clan is equivalent to rebellion!
The Five Founding Dukes were reluctant to back down, even indignantly believing that everyone couldn't be blind, could they really not see that this was a conspiracy by Owen Bertram against the five families?
