A Past to Be Erased

is episode 215 of the original Naruto anime.

Synopsis
When Menma is injured by one of the bandits, it is revealed that he was once one of them, and that he was at the town during the attack. Despite this, Menma is willing to risk himself to help fight off the bandits, and tells Naruto of the leader's master plan to flood the town with a dam. After revealing that he never lost his memory, Menma sacrifices his life to cause a rockslide to save the town. Naruto defeats the bandit leader and mourns Menma's loss.