Naruto Shippuden Episode 40 & 41

Title: "The Nine-Tails unleashed!!" & "Top-secret mission starts"
Date: December 20, 2007

Immediately after Yamato signals Naruto and the others out to the bridge where Orochimaru and Kabuto are waiting, Naruto's chakra begins to boil with the chakra of the Nine-Tailed Fox. Slowly, Naruto grows more tails as Orochimaru taunts him and makes him even more angry. Meanwhile, Yamato remembers Jiraiya speaking of how many tails he has seen Naruto grow. Jiraiya explains more about what happened and more about how Naruto acts when he's in his Nine-Tails form.

Naruto continues to get even more enraged and easily counters Kabuto's attack, flinging him away. Naruto's counter throws Kabuto into Sakura, knocking her unconscious. Orochimaru continues to watch Naruto become more enraged, eventually destroying the Bridge of Heaven and Earth. As the bridge collapses, Sakura slides off the edge. Sai draws a bird to fly, but chooses to follow Naruto and Orochimaru instead of saving Sakura. Yamato saves her at the last second, and creates a wood clone to catch up to the battle. Eventually the fourth tail appears, allowing the vile chakra to completely control Naruto's body, forming him into a miniature Nine-Tailed Fox.