honestly, the Woosan (Wooyoung x San) fics dominate the platform for a reason. It's that specific energy—the chaotic, performative intensity they have on stage gets translated into these incredibly high-stakes narratives. Writers latch onto their 'demon line' personas and run with it, crafting dark fantasy AUs or intense rivals-to-lovers arcs. You'll find a ton of werewolf/vampire universes or mafia settings built around them.
Mingi and Yunho, often tagged as '2Ho' or 'Yungi,' have a huge following for fluffier, domestic stories. Their real-life friendship reads as incredibly solid and warm, so fanfiction tends to explore established relationships, college AUs, or just soft, slice-of-life stuff. It's the comfort read section, less about external plot and more about the cozy dynamic.
Seonghwa and Hongjoong (Seongjoong) are big for more complex, slow-burn plots, often with a power dynamic element—captain and first mate, CEO and assistant, teacher and student. The appeal is the built-in tension and eventual deep loyalty. I'd say Woosan fics get the most sheer volume, but Seongjoong stories often have the most elaborate world-building.