360 Degrees of Vision: The Byakugan's Blind Spot

is episode 116 of the original Naruto anime.

Synopsis
Kidōmaru managed to shield himself from Neji's attack, and fled to the safety of the neighbouring trees. Deciding to attack Neji from a distance, Kidōmaru advanced his cursed seal to its first level before sending multiple spiders to attack Neji. Neji was able to repel them all, although Kidōmaru noticed a delayed reaction in some of Neji's blocks. He theorised that Neji's defences had a blind spot, and continued to attack him from this blind spot. His theory was proven correct, as Neji was unable to block the attack. Believing himself to have found Neji's weakness, Kidōmaru prepared himself to finish the battle.