Urokai sure hate Frankenstein. Now his actions in the past come as no surprise to me. No wonder when they fight Urokai was so vises. He does hate Frankenstein to the guts. And most of them liked Raizel a lot. Who convinced them to betray him like that. I think that this flash back is gonna show us the story from where it begun. I really think something must have happened to those nobles or some event appeared who knows but there have to be a very good reason for their betrayal.
So I think in the next chapters Frankenstein will form a contract with Raizel. That would piss off Urokai and the other betrayers and with a little push from someone we don't yet know about they will try to kill Raizel nim. Oh the other interesting thing how the hell did they put him in that condition that he had to fall asleep for 700 years. And my apologize but where the fuck was Frankenstein at the time. How the hell he let that happen?
At least that is my guess. So we will have to wait and see.