Honestly, I've got complicated feelings about Michael/William dynamics. Sometimes writers set them up as this epic binary—sunshine vs. shadow, jock vs. scholar, that kind of thing—but the best fics I've seen ditch the obvious rivalry tropes. Instead of constant head-butting, you get this slow-burn realization that they're competing for the same space in a friend group or a family's approval, which feels way more grounded. The rivalry isn't about hating each other; it's about two people who understand each other's drive a little too well, which makes the friendship that develops stingier and more significant.
I read one where they were rival apprentices in a fantasy AU, and the entire plot was them secretly trading notes to outdo their master, not each other. The friendship emerged from shared resentment, not admiration. That felt true to life. Rivalry born from similarity is more interesting than from difference. They become allies against the world, then friends, then sometimes something else entirely if the ship goes there.
It's the subtle shifts that get me—a handoff of a book with underlined passages, covering for the other's mistake, realizing the competition was just a structure they both hid behind. The rivalry isn't erased; it becomes their private language.