It's funny, because I actually think a lot of the fics that get tagged under that pairing aren't really about romance at all? They're using the ship framework to dig into their bond, which is so specific and brutal. Like, you have this kid who absorbs death and this other kid who commands it, and they're both just... broken in complementary ways. The good ones don't make it sweet; they make it about the weight of shared trauma. Megumi carrying Yuji's body after Shibuya is the ultimate fanfic fuel, and the best stories capture that awful, tender responsibility. They'll write these quiet scenes where they're just sitting in silence after a mission, and it's not about holding hands, it's about acknowledging the other person is the only one who gets the particular flavor of hell they live in.
I've read a few that completely flip the expected dynamic, too. Where Yuji isn't the sunshine ball and Megumi isn't the aloof emo. Megumi is fiercely, practically protective, and Yuji is quietly, deeply observant of Megumi's isolation. The friendship feels earned because it's built on recognizing the other's strength, not just their pain. The fics that work best for me are the ones where their loyalty is a choice they keep making, even when it costs them everything. It's less 'will they kiss' and more 'will they survive each other's destinies,' and that tension is everything.