Sasuke Recovery Mission

The Sasuke Retrieval arc spans from chapters 172 to 238 of the manga and episodes 107 to 135 of the Naruto anime. It is the last arc of Part I.

Background
After Itachi Uchiha mentions Sasuke Uchiha as "weak", he wants to seek more power. In addition, Sasuke becomes envious of Naruto's rapid improvement, which is confirmed in their fight on the hospital's rooftop. Earlier during the Chunin Exams, Orochimaru offers Sasuke more power to kill his brother. Later he sends Sound Four to further extend the offer, Sasuke later on takes this offer and decides to leave Konohagakure for Otogakure.

Synopsis
Shikamaru Nara is coincidentally appointed Chunin when Sasuke leaves the village. His first mission was to gather a group of Genin to bring Sasuke back to Konohagakure. He gathers Naruto Uzumaki (per Tsunade's request, who also promises to Sakura Sasuke's return), Neji Hyuga, Kiba Inuzuka, and Choji Akimichi. They easily catch up to the Sound Four, who are guarding Sasuke. Jirobo and Choji stay behind and do battle while Team Shikamaru catches up to the other members of the Sound Four. Choji wins his battle, but due to the effects of the Three Colored Pills, he is too injured and can't go on. The same thing happens to Neji; he stays behind and fights Kidomaru. Kidomaru, at one point in the fight, eventually discovers the blind spot of Neji's Byakugan and immediately turns the tables. Neji, however, with some emulation of Naruto's determination, uses his blind spot to his advantage, and strikes Kidomaru with Gentle Fist, winning the fight, but is severely injured and can't continue. Shikamaru, Naruto, and Kiba catch up to Sakon and Tayuya, but an exploding tag explosion separates Kiba, his dog Akamaru, and Sakon to an underground location. Kimimaro arrives and takes Sasuke's coffin, with Sasuke in it the whole time.

Kiba and Akamaru do battle with Sakon and his brother, Ukon, and Shikamaru fights Tayuya. Naruto follows Kimimaro and they eventually do battle. Kimimaro proves to be far superior to Naruto, and just as he is about to deal damage himself, Rock Lee soon arrives and tells Naruto he'll fight Kimimaro and Naruto can chase Sasuke (who awoke from his coffin during the battle). Kiba and Akamaru, despite their most powerful attacks, prove to be no match for the siblings, and are about to be killed by Ukon. Shikamaru, despite his strategical prowess, also falls at his opponent's mercy, and Lee is about to die at Kimimaro's hands. Fortunately, Tsunade who had contacted Sunagakure earlier to assist in the mission enable Team Baki to appear and save the ninja. Temari defeats Tayuya, Kankuro defeats Sakon and Ukon, and Gaara does battle with Kimimaro. Kimimaro's kekkei genkai allows him to defeat Gaara's sand jutsu, and at the end of the battle, Kimimaro is about to deal death to Gaara and Rock Lee when he finally succumbs to his terminal illness.

Naruto vs Sasuke
Naruto catches up to Sasuke and they do battle. Sasuke's Cursed Seal of Heaven, which had been powered up by a pill given to him by the Sound Four (this was why he was in the coffin), gives Sasuke inhuman strength, which he uses to reduce Naruto to almost rag-doll levels. Meanwhile, Sasuke recalls his experiences with Itachi and his parents up to the point of the Uchiha Clan Massacre. It is in these memories that the Mangekyo Sharingan and how Itachi obtained it (by killing his best friend, Shisui Uchiha) is revealed; it is also revealed that Itachi had encouraged Sasuke to gain the Mangekyo Sharingan, the only way he could exact revenge on Itachi, by any means necessary, and this becomes Sasuke's motivation for killing Naruto, who he claims to be his best friend.

Back in Konoha, Kakashi Hatake, put up to speed on the situation, summons his ninken to track down Naruto and Sasuke, including Pakkun. Meanwhile, Naruto and Sasuke unleash the Rasengan and Chidori respectively, causing each other to fly backwards. Activating his Cursed Seal, Sasuke uses his enhanced speed and strength to overcome Naruto and strike him with a Chidori. Naruto manages to block the attack, but Sasuke, still intent on killing Naruto, tries to strangle Naruto, only to have himself thrown aside by a demon-fox powered opponent.

With his enhanced abilities, Naruto easily overwhelms Sasuke, and tries to reason with him, only to have Sasuke ultimately reject his efforts, though Sasuke finally admits they're fighting as equals. In this moment, Sasuke's Sharingan finally matures, enabling him to predict Naruto's movements and once again turn the tables. Upset by Naruto's persistence, Sasuke knocks him unconscious with Peregrine Falcon Drop. The Nine-Tailed Demon Fox, probably to save itself, gives Naruto even more of its chakra, creating, for the first time, the second stage of Naruto's demon fox transformations, the one-tailed demon fox's cloak. With one arm of the cloak, Naruto unleashes powerful short and long-range attacks, which Sasuke, even with his Sharingan, cannot keep up with.

Feeling he has no choice, Sasuke increases his Cursed Seal of Heaven to Level 2, once again evening the playing field. Both Sasuke and Naruto realize the cost of their respective abilities at that point, but both decide that they have no other choice. Sasuke reveals that the location of their fight is the Valley of the End, and determined to end the battle, forces the use of a third Chidori. Naruto creates, using one hand, and the cloak's chakra as a shell, a purple Rasengan. Sasuke's Chidori, after a moment, warps into the Flapping Chidori. The two ninja collide their attacks; Sasuke, planning to punch Naruto in the heart, deliberately misses and targets the gut instead, while Naruto, referring to one of Sasuke's insults, scratches his headband. A black dome of energy forms around them, which eventually dissipates, revealing the two ninja as their current forms, and then as their childish forms, who hold hands and smile. When the dust settles, Sasuke comes out victorious.

Sasuke ponders whether to kill an unconscious Naruto, but decides to leave him alive in the end. Kakashi and Pakkun arrive; disappointed they were too late, Kakashi takes Naruto back to Konoha. At the same time, Sasuke decides to gain the power to kill Itachi his own way, through Orochimaru, as he walks off to Otogakure. It is then revealed that Akatsuki member, Zetsu, was watching the fight the whole time.

Ending
As Kakashi takes Naruto back to Konoha, several medic-nin appear to update him on the situation and to take care of Naruto "and Sasuke", which Kakashi deems unnecessary for obvious reasons in both cases. Neji and Choji both undergo intensive medical treatment; both are successfully healed, though Choji would have died if it wasn't for the Nara Clan's medical tome and Tsunade's medical prowess. Kiba and Akamaru heal from their moderate injuries, under the care of Hana. Shikamaru, with his only his finger injured, decides to end his ninja career, as he put his team's life in danger and his mission failed, but Shikaku convinces him to persevere. Sasuke is shown walking with Orochimaru and Kabuto in one of Orochimaru's lairs.

Shikamaru pays Naruto a visit in his room, while Sakura decides to visit Naruto "and Sasuke", only to be severely disappointed by Naruto's failure to bring Sasuke back, as she overheard Naruto and Shikamaru's conversation. Naruto, however, declares his promise to keep to his original promise, to which Sakura gratefully responds. After her visit to Naruto, Sakura, realizing how useless she had been in keeping Sasuke in Konoha, requests Tsunade to take her on as her apprentice, to which Tsunade consents. Naruto's next visitor is Jiraiya, who reveals that Orochimaru had already taken a body before Sasuke arrived (so he has to wait another three years to take another body) and tries to convince Naruto to give up on Sasuke, based on his similar experience with Orochimaru. Naruto, however, refuses to quit his efforts. Jiraiya, who figures it pointless to change Naruto's mind, decides to train Naruto for two-and-a-half years, to prepare Naruto for the Akatsuki, which Naruto readily accepts.

In the anime, Naruto is forced to remain in Konoha for a few months before setting out with Jiraiya. In the manga, he leaves as soon as he gets out of the hospital. Sakura also asks to become Tsunade's apprentice at a later point in the anime.

Trivia

 * Naruto's only loss in the series is during this arc