The title refers to Hiruzen’s deep regret over failing to kill Orochimaru years earlier. A flashback shows Hiruzen discovering Orochimaru ’s illegal experiments on human test subjects. Despite having him cornered, Hiruzen’s affection for his favorite student stayed his hand, allowing Orochimaru to escape and eventually return to destroy the village.

In the Naruto episode (English Dub Episode 72), the climactic battle of the Konoha Crush arc reaches a chilling turning point as the Third Hokage, Hiruzen Sarutobi , faces his former student, Orochimaru .

After summoning the First and Second Hokage to fight for him, Orochimaru reveals the true extent of his immortality research. He literally peels away his own skin to reveal the face of a young woman. This confirms his technique, which allows him to cheat death by periodically transferring his soul into a new "vessel". He explicitly states that his next intended target is Sasuke Uchiha . A Mistake from the Past

The episode centers on two major revelations and a desperate final stand: