I dunno, I'll have to let it percolate a while longer before I figure out if there's any real meat to it. Sometimes I get vivid pieces of fic, but the whole thing never comes together.

I also like the idea of Jack being, like, the only hunter ever that John can't infuriate into chasing him off. John does his best to push people away and he is so good at it, but Jack wouldn't let him. He sees right through that sort of thing. He's quite uniquely suited to handle John's boatload of issues, and John's not used to people who know how to deal with him.

And of course in the background there's all this plot going on. I'd have it be supernatural and not aliens, because by now Jack would know at least something about supernatural stuff and because introducing aliens to John would mess with him too much. Best to keep things relatively simple for him. Though that would raise, so to speak, the question of how Jack would explain his not-dying thing, since no hunter worth his salt would buy, "Oh, it wasn't as bad as it looked."