"Their Backs" (二人の背中, Futari no Senaka) is episode 409 of the Naruto: Shippūden anime.
As Chōji, while under the control of Saya's Puppet Imitation Technique, charges at Sakura, Ino takes over her foe's control over her team-mate and charges at Team Saya instead. Mamushi and Sana manage to avoid the attack, but Saya takes the full blow, what was later revealed to be a Body Replacement Technique. Taking the look of her puppet, Saya manages to regroup with her allies, claiming that she doesn't care about the Chūnin Exams anymore and that she wants revenge. As Team Asuma head toward the main tower, Sakura begins thinking about how weak she was before and that she always needed Naruto and Sasuke to protect her. At the same time, Jiraiya is seen training Naruto, asking Gerotora to weaken the seal on Naruto's belly. As the seal weakens, the boy falls under the control of the Nine-Tails, manifesting four tails and attacking his master. After the fight, the two are seen laying in hospital beds, with Naruto apologising about what he had done to Jiraiya, only for him to say that it wasn't his fault. As Jiraiya asks whether the boy will give up, Naruto tells him that he won't, even if it'll seem impossible. Meanwhile, Sana uses her Sandstorm Technique to stop Team Asuma in their tracks. As the team realises that the sandstorm is unnatural and that someone is after them, Saya uses her Cursed Sand Puppet Technique to create sand dolls in order to attack and confuse her foes, with Sana using her Sand Cloak Technique to disguise Mamushi as one of the creations. As Chōji fends off the dolls, one of them turns out to be Mamushi, who uses hissnake to poison both him and Ino. Sakura, recalling her surgery and the request to Tsunade for an acceptance in the Chūnin Exams, manages to replenish her chakra and finish off her foes in one blow. She then removes the poison from her allies and thanks them for letting her join their team.