It's honestly the vulnerability they let each other see. In most canon settings, these two are presented as these untouchable idols, always composed and perfect for the cameras. Fanfiction strips that away. The 'hot' stories that stick with me aren't just about physicality; they're about that first crack in the professional facade. Maybe it's exhaustion after a long schedule, a moment of doubt shared in a dark practice room, or just the sheer relief of dropping the act with the one person who truly gets the pressure.
That charged familiarity is the real catalyst. When a story nails the tension of years of built-up understanding suddenly tipping over into something else, the physical scenes feel earned. It's not random; it's the culmination of all those silent glances and secret inside jokes finally boiling over. The 'NC' label almost becomes secondary to that emotional payoff—the heat comes from the release of all that suppressed, long-term tension. I've clicked away from plenty of fics that were just gratuitous; the ones that linger are the ones where you believe the characters would actually break that boundary, because the story made their connection so palpably real first.
That shift from 'partners' to something more feels like a secret the reader is in on, and that's a huge part of the appeal.