Frankly, I think the fascination sits squarely on power dynamics and intellectual friction. Hermione's righteous, brilliant moral compass grinding against Lucius's aristocratic, cynical worldview creates a perfect storm. It’s not just 'enemies to lovers'—it’s ideological warfare turning into something else. The best fics explore the sheer improbability of it, the slow erosion of prejudice, the shock on both sides when they recognize a formidable mind in the other.
You see a lot of wartime or post-war AUs where Lucius, stripped of wealth or influence, has to engage with her on a different level. Or time-travel where a younger Hermione meets a pre-Fall Lucius, and the tension comes from her knowing his future while being drawn to his present charm. The theme of 'redemption through her' can be heavy-handed, but when done well, it's about him redeeming himself for his own sake, with her as the catalyst, not the prize.
Less discussed but equally compelling are fics where Hermione embraces a darker, more politically ruthless side, and Lucius is the only one who can match that. The theme becomes 'corruption' or 'mutual understanding in ambition,' which flips the usual moral hierarchy. It’s a pairing built on a thousand conversations, secret glances across a gala, and the terrifying realization that your greatest adversary understands you best.