Honestly I always go back to the Pain fight. That's the moment it stopped being about a kid with a weird power and became something else entirely. Seeing him come back after Hinata's sacrifice, the way the rain literally reversed direction, the complete silence except for that low hum of chakra. It wasn't just power, it was a tone shift. The whole village watching, Kakashi thinking he failed, and then Naruto just... arriving. He didn't even look angry, just utterly resolved. The Six Paths mode later is flashier, sure, with the floating orbs and the truth-seeking balls, but that first Sage Mode entrance against Pain? That's iconic for a reason. It felt earned, and desperate, and like the entire story had been building to that single walk out of the smoke.
People talk about the final battle with Sasuke, and yeah the visuals are insane, the valley gets re-sculpted, but emotionally it's a different beast. It's two gods fighting over philosophy. The Pain fight was Naruto becoming the protector he always said he'd be, on a scale he never imagined. I still get chills when he deflects that massive chakra blast with a single rasengan after nailing all the bodies with clones. The animators went so hard on that sequence, you could feel the weight of every hit.