[Castiel actually knows about Kurotsuchi, actually; Raven told him, and warned him of the potential risk. But if it comes to it, he may seek out the shinigami anyway and attempt to finagle a suitable agreement.

Despite the tone of Rei's question, Castiel is calming down from his anger now that they've moved off the topic of the souls, and onto a less moral and more logical one.]

It isn't simply for revenge. I have to gain an advantage here, or I will have absolutely no standing; as it is he's violated our agreement and there's nothing I can do about it as I have no leverage at all. I can't allow him to do whatever he likes with no opposition or he'll simply continue to do so.