For some reason Frankenstein is going easy on that creep. I think he wanted to see Urokais soul weapon. Frankenstein seems to have motives for everything. He is just too smart he takes advantage because the other Nobless are misjudging him. Urokai still have the pedant or whatever that think was. That is somehow connected to Frankenstein's past. Maybe a woman, sister mother. Probably we will have flashback in the flashback.
But still we don't know why Frankenstein wasn't with Raizel when they acceded him. And why didn't Raizel fight back. And Frankenstein's past is just too interesting. I really really want to know what happened with him.