It's weird to think that the first fight between Naruto and Sasuke in the Valley of the End happened a little over 10 years ago now, so it's technically a Throwback Thursday, though it doesn't feel that way somehow.
This was the second fight between Naruto and Sasuke, and really the first MAJOR fight. We see both of our beloved heroes go toe-to-toe at the base of the waterfalls in the Valley of the End
It's the first time we see Naruto utilize a Kyuubi form, unleashing the 9-tails' chakra in the one-tail form. With it, he's able to override Sasuke's Sharingan and it's ability to perceive future moves.
THEN SASUKE GROWS THE WEIRDEST GODDAMN HAND WINGS EVER
The instance where Chidori and Rasengan meet is an image for the ages.
Resulting in this, the weirdest unexplained phenomenon in the entire series.