Thats kinda easy and a hard requirement, for thr Tang empire it is easy to do so bjt for the rest of the guilds they probably have a hard time unless they know the requirement and decided to assassin ones of the Kings.
All kings know this requirement but the players don’t so unless a group just wantonly kill everyone on the floor until they succeed or have leverage over a king. So yea has you said it’ an easy and hard requirement indeed