look i just think that Dean, eventually, would have sat Cas down in the Dean-Cave to watch Lord of the Rings with him (because they're amazing films). And they'd get to Rivendell, and Arwen would give Aragorn the Evenstar pendant and Dean would remember and be like oh shit. and that line - the "it was a gift. keep it" - that doesn't come yet for a few scenes and Dean would be sitting there sweating.
But Cas. Cas wouldn't be paying that much mind at all. Because honestly I don't know that he'd pay a terribly large amount of attention to the films at that point, not the beginning. It's charming and all, but not especially interesting. He watches most of whatever Dean asks, because Dean enjoys them and Cas wants to spend time with him. But he usually pays more attention to Dean than to whatever is on the screen. Until Dean starts acting kinda cagey and weird and then Cas starts paying more attention to the couple on screen - this ethereal immortal elf and her human warrior lover. And this question of if she would give up immortality and her people to be with her lover, that would catch his eye.
And I think that maybe Cas wouldn't really catch on at first, he'd pay attention through the Council of Elrond and nod along like ah yes, a heroic quest to stop evil, i understand why Dean likes this now. And the movies would continue and he'd pay attention, but I think Arwen would stick in his mind even though she doesn't get a lot of screen time. He doesn't say anything about the mixtape or the Evenstar but he's paying attention now and Dean is still sweating.
When Eowyn comes in Cas likes her, and he respects her, but he also seems so disappointed, because its clear that she's interested in Aragorn, and surely that's a better match, right? Like Aragorn would have more in common with a human, and she's brave and free-spirited and amazing, of course he's likely to end up with her instead. It makes sense and it makes Cas heartsick. And they'd reach that point in the films where Elrond is trying to persuade Arwen to leave, the point where she turns back, and suddenly Cas is riveted. He has to know what happens to her. He has to know if Arwen lives, if Aragorn will reciprocate Eowyn's feelings, or if Arwen and Aragorn get to be together after all.
And when she appears at Minas Tirith I think he'd burst into tears i.e. tears just pouring down his face while he stares at the screen oblivious that he's even crying. And Dean is like righteously freaked out at this point because he's watched a ton of movies with Cas and his reactions always vary, anywhere from confused disinterest to mildly engaged but he's never seen Cas so moved by a piece of film before. And Dean can't even pay attention to the end cause he's busy watching Cas. And Cas has never resonated so much with a fictional character in his life as Arwen Undómiel.
And Dean's like, still mildly concerned as the credits for RotK roll and is like "How'd you like it buddy?" and Cas is so serious and so heartfelt when he tell Dean that he loved it and thanks him for sharing it with him.
idk where things go from there i just keep envisioning this from time to time Castiel is Arwen-coded ty for coming to my tedtalk
