Naruto: Shippūden (2007)

S06E136 The Light & Dark of the Mangekyo Sharingan

Itachi discloses to Sasuke that Madara played a significant role in the Uchiha massacre and shares the backstory of the Mangekyo Sharingan, mentioning that the first two to wield it were Madara and his brother. However, one mystery lingers: what was Itachi’s true motivation for sparing Sasuke's life?