Right off the bat, Nagi mentally equated Wesker with the man who was responsible for the deaths of his wife and unborn son. :| So. That was a good start. He considers Wesker a potential threat and wouldn't hesitate to take him on if he had to, though he's not sure he would win in a fight. He feels like he needs to know more about Wesker's abilities before taking any sort of action other than just keeping his eye on him, though he considers his need for the serum a possible weakness that might be exploited.

To Karkat, Wesker's much more like a troll than most other humans, so he's much easier to understand than most humans. Which makes him a little weird as a human, but fine in general. The throwing a knife not-quite-at-him was alarming, but honestly, Karkat's used to people who like him being violent toward him, so this isn't really outside the norm at all. Honestly, as far as Karkat's concerned, this is the beginning of a very nice bro-ship.