Sasuke's rivalry is what gives 'Naruto' its backbone, I think, but not always in the ways people celebrate. Early on, it's straightforward: Naruto wants to surpass him, Sasuke sees Naruto as a nuisance but also a mirror to his own loneliness. That dynamic drives the first major arcs—the Chunin Exams, the retrieval mission—and it's compelling because it's personal. But after Sasuke leaves the village, the rivalry becomes this strained, long-distance thing. The story keeps cutting back to him, but he's off on his own grim quest for power, and Naruto's obsession starts to feel a bit one-sided for a long while. It creates a weird pacing issue where the main character is chasing a ghost who's barely interacting with him directly.
Where it really shapes the arc, though, is in the final act. All that buildup about bonds and hatred comes to a head when they finally fight at the Valley of the End the second time. Without that foundational rivalry, the themes about breaking the cycle of vengeance and finding connection wouldn't land as hard. Sasuke's path forces Naruto to constantly question his own ideals and what he's willing to do to save a friend who's become an enemy. Honestly, sometimes I found Sasuke's choices frustratingly edgy, but you can't deny they made Naruto's eventual victory—and Sasuke's eventual surrender—more earned. It’s less a classic rivalry and more a tragedy that the story bends itself around until it snaps back into place.
A smaller thing I notice on re-reads: their rivalry also elevates the side characters. Sakura, Kakashi, even the rest of Team 7 get pulled into its orbit, and their reactions add layers the main duo couldn’t provide alone. It’s messy, but it’s the engine.