As much as Soushi might say otherwise, the fact was that he did have demon blood in him. That wasn't something Castiel could ignore until he was absolutely certain it wasn't going to be a problem later on. He was friends with a human who had demon blood, and Sam was someone he trusted -- but Sam had also earned that trust.

Soushi seemed to be genuine with what he said, but Castiel wasn't quite willing to let his guard down just yet. He doubted that it would turn out that Soushi had ill intentions all along, but it was better to be cautious about this for now.

While Soushi made an offer for them to travel together, he did it while looking away at something. Castiel glanced in the same direction, but didn't see anything of interest. It made him wonder why Soushi didn't keep eye contact at that point, but body language wasn't something he relied on too greatly when it came to reading people.

"Accompany me? Where would you wish to go?" Castiel had to admit that he hadn't had a solid plan on where to search the institute in some time now. Soushi was new and therefore he wouldn't have much insight on where to search, but Castiel was still curious to hear about it.