"Light vs. Dark: The Two Faces of Gaara" (光と闇 我愛羅という名, Hikari to Yami Gaara to Iu na) is episode 77 of the original Naruto anime.
As Gaara continues to reminisce about Yashamaru, he remembers Yashamaru's defeat and attempted suicide bombing. Yashamaru tells him that Gaara's father, The Fourth Kazekage, ordered him to kill Gaara. He also adds that while he could have refused the order, he wanted to kill Gaara because he hated Gaara for causing his sister's death. Yashamaru then opens his flak jacket and reveals explosive tags on his torso, which detonates. Although he was able to survive the blast, Gaara lost the only person who he thought ever cared for him, who revealed that he never did love him at all. From that point on, Gaara came to love and care about only himself, and starting living off of killing others, believing that to be the purpose of his existence.
Returning to the present day, Gaara quickly restrains Sakura with a claw made of sand and slowly squeezes her. He detaches the arm holding Sakura and regenerates it, and continues to transform further into Shukaku. Now having no more humanoid features, Gaara resolves to kill Naruto as well, all the while telling Naruto that he must fight for himself and not for his friends. Determined to save Sasuke and Sakura at all costs, Naruto attempts to summon Gamabunta, but ends up summoning Gamakichi, a smaller toad who is unable to fight. Gaara then launches Sand Shuriken at them; Naruto manages to save Gamakichi as the shuriken pummels him. Naruto realises that Gaara is lonely, just like how he used to be before he met Sasuke, Sakura, Kakashi and Iruka, and wonders if he would have ended up like Gaara had he not met them. Thinking back on how meeting his friends gave him happiness and saved him from darkness, Naruto resolves to save them from Gaara, even at the cost of his own life.