Kakashi's Anbu Arc: The Shinobi That Lives in the Darkness

The is the seventh filler arc from Part II of the series and spans from episode 349 onwards. The arc focuses on Kakashi Hatake's ANBU background, taking place after the battle at the Kannabi Bridge, losing his closest friend Obito Uchiha, and later taking Rin Nohara's life with his own hands. This arc takes place in the middle of the Ten-Tails Revival Arc.

Summary
The previous Ino–Shika–Chō is sent out to complete an Iwagakure treaty mission. Iwagakure doesn't intend to keep a peaceful treaty, but as the meeting happened at the border with the Land of Wind, the Fourth Kazekage ensured no fights would break out near his country. The Iwagakure-nin return and update the Third Tsuchikage about the events. In Konohagakure, Kakashi still feels guilty about his role in Rin's death. In a meeting with the council, Hiruzen decides to step down in favour of a new Hokage.