Hashirama's Cells

is episode 351 of the Naruto: Shippūden anime.

Summary
Kakashi is still plagued by nightmares and as a result become even more sullen than before. Seeking answers about Kinoe's abilities, he breaks into the Hokage Residence where he is caught by Hiruzen. The Third explains a bit about the history of Hashirama Senju along with the village's initial experiments to keep the Wood Release kekkei genkai alive, and the subsequent disappearances. Elsewhere Danzō plots to have Hiruzen assassinated on his way to the Fire Daimyō, however, his plans are foiled when Kakashi warns the Hokage of the plan. During their brief confrontation, Kakashi releases Kinoe informing him that one day his abilities would prove useful to the village. Letter reporting to Hiruzen, Kakashi ultimately accepts a post as an ANBU under the Third's direct command before informing him of Kinoe's existence. The youngsters of the village all discuss the changes that had once again been made and despite being saddened that Minato had passed, still wished the best for Hiruzen and then future of the village.

Trivia

 * In the scene when Kakashi is reading about Hashirama Senju and the Wood Release, one of the dead shinobi in the flashback images greatly resembles Sasuke Uchiha.