I have two:-
1. RM guy from BTS and Rosé girl from blackpink, i think a chill slow song with maybe minimal instruments would suit both of them. I think their voices would match very well in that concept.
2. Baekhyun guy from exo (almost wrote becon) and jhope guy from BTS. Some sort of sad angry vibe or happy sarcastic song would be good and match both of them, tbh these two are very versatile in my knowledge, I think the mentioned song would suit them.
As my knowledge pool in kpop is small, I don't know many artists name of song even if I listened to them in someone else's playlist.
Let me know yours choice and concepts.
