Inside the Mist

is episode 100 of the Naruto: Shippūden anime.

Synopsis
Guren is rendered unconscious and relives her past as Naruto is caught in an illusion about Sasuke. After Kakashi finds him, Teams Kakashi and Team Kurenai conclude the mist around them causes Genjutsu courtesy of the Three-Tails. After Guren wakes up, Yūkimaru suffers another fever and passes out. Tsunade hears of the Three-Tails and assembles Shizune, Ino, Tenten and Lee to go and seal it before the Akatsuki do. Naruto and Sakura talk about the home that people should return to before Naruto heads off to find Yūkimaru.