Responses
Basically the grand dukes are the kings of the empires devoured by that monster. The planets and the people of that planets, including the kings/grand dukes, are already all dead but they are "resurrected" to play the game since they want to destroy the monster that ate their world.
Hope it's clear, if you have any question lmk!

I’m a little confused with these last two chapters…. What exactly were the guides talking about in terms of the grand dukes?