i can't stop thinking about them being on a hunt, taking down a vamp nest, or a bunch of werewolves, or something else that runs in packs. and dean and cas have just gotten together, so they're in that stage where everything is new and exciting, but it also means they're much more aware of the dangers the job poses to each other. and they're fighting, and there's blood and claws and teeth everywhere, and they're on opposite sides of the battle. and sam is there, maybe even donna and jody, or garth too. a bunch of hunters versus and bunch of monsters. and both cas is just focused on getting his part of this job done, when he suddenly hears it. in his mind, it's dean whispering to himself "please don't let cas get hurt, please don't let cas get hurt. i've only just gotten him, please don't let me lose him now." and it ticks something in cas. so his sole focus is to get this done so he can get back to dean. but of course he's rattled, and completely taken aback that instead of dean turning off his head and acting on instincts like usually in battle, he's there thinking of, literally praying for cas not to get hurt. so the monster catches cas off guard and it's a whole big deal of dean storming from end of the field to the other, chopping off head before falling to his knees to check on cas. and dean cups his face and cradles him in his arms, kissing the top of his head, going "how the hell could this happen? why weren't you focused? you blink and they get you!" and it opens for the news that cas can hear dean praying when they're in battle and it's awkward, but eventually they find a way to use it to their advantage instead of a liability.