Honestly, I'm not entirely convinced he's the definitive lead, even though the story frames him that way. Usui's the 'perfect' student on the surface—top grades, athletic, impossibly good-looking—but the core of his role is as a chaotic catalyst and a deeply bored observer who finds his entertainment in the female lead, Misaki. He's less a romantic hero from the start and more like a capricious, slightly predatory force of nature who decides to 'tame' her. That dynamic is everything; it flips the usual shoujo script where the girl pines. Here, he's the one utterly fascinated, and his 'hotness' is almost a weapon he wields with detached amusement until his own feelings catch him off guard.
What's really compelling is how his archetype plays out. He's the 'Cool Prince' trope, but they constantly subvert it by making him genuinely weird, stalker-ish at times, and with a mysterious, hinted-at dark past that never fully consumes the plot. His role isn't to be a knight in shining armor. It's to be a mirror and a challenge, pushing Misaki to acknowledge parts of herself she denies, while his own cold exterior slowly thaws because of her relentless normalcy. His 'hotness' is the initial hook for readers and characters alike, but the story makes you stay for the cracks in that perfection.