As it stands, this is not cooperation, nor is it a way to collaborate in the future. It's extortion, a one-sided form of coercion.
But it doesn't matter, there's no problem at all. Since Brian's greatest vulnerability is in the hands of the Black Devil, both Brian and Yang Yi can just bow and scrape; they have to ask for favor with a lowly attitude.
No matter by what means or what posture they adopt, as long as they can learn the whereabouts of Annastasia, and once they get to see Annastasia, then everything is negotiable.
As for what to do after finding Annastasia, that still depends on Yang Yi's needs.
There's a saying that goes, "When you gaze long into an abyss, the abyss also gazes into you." While spying on the Black Devil, the Black Devil will certainly also spy on the Organization of Water.
