The Battle

As Sasuke was defeating Orochimaru, Itachi sensed something odd. Kisame asked him what was wrong, to which Itachi replied, "No, it's nothing." Following Kisame's capture of the Four-Tailed Monkey, Itachi and Kisame met with the rest of Akatsuki. There, they discovered that Sasuke, after being trained by Orochimaru for two and a half years, had killed his teacher. Sometime after the Four Tails was sealed, Zetsu informed them that Sasuke had been killed by Deidara's C0. Kisame asked Itachi if he was upset that Sasuke's death had left him as the only Uchiha because in the rain he looked as if he were crying. However, Itachi remarked that Sasuke wasn't dead, and alluded to the fact that there was still another Uchiha regardless.
Knowing that his end was near, one of Itachi's shadow clones confronted Naruto, who was looking for Sasuke. Although he claimed he wished only to talk, Itachi was forced to defend himself against Naruto's attacks. After fending off Naruto, Itachi asked why he showed so much interest in Sasuke, a traitor to Konoha. Naruto replied that he was more of a brother to Sasuke than Itachi had ever been, and that he would do whatever it took to bring Sasuke home. This caused Itachi to give a small smile, followed up by asking if he would always feel that way, even if Sasuke attacked Konoha. Naruto replied only that, if that happened, he would stop Sasuke without killing him and protect the village. Content with this answer, Itachi gave some of his power to Naruto, by forcing him to swallow one of his crows, and hoped he would never have to use it.
After his business with Naruto was done, another of Itachi's shadow clones went to meet with Sasuke. Sasuke exhibited a dramatic improvement in his abilities during their confrontation, so Itachi agreed to have their final battle at the Abandoned Uchiha Stronghold. He waited there for Sasuke's arrival, instructing Kisame to not let the other members of Sasuke's team interfere with their combat. Itachi and Sasuke met face-to-face and, while exchanging genjutsu, had a conversation about the Uchiha, Madara, and Itachi's "true" motives of wanting to take Sasuke's eyes. When Sasuke managed to escape Itachi's Tsukuyomi, the genjutsu battle ended and the ninjutsu battle began.
Itachi used Amaterasu, but Sasuke shielded himself by shedding his skin, a technique he was able to use due to Orochimaru being sealed within him. Using the shed skin as a decoy, Sasuke went below and fired a Fire Release: Great Dragon Fire Technique at Itachi's direction above although he only managed to burn away one of Itachi's sleeves. Out of chakra, he told Itachi about his final jutsu that, like Amaterasu, is impossible to avoid. Sasuke then used his trump card, on Itachi, who got his Akatsuki cloak burned off as a result.^[13]

Itachi faces Orochimaru's Eight Branches Technique.

Added by Omnibender

However, Itachi managed to survive by using Susanoo to defend himself. With Kirin having expended all of Sasuke's chakra, Orochimaru was able to break free and violently appeared through his Eight Branches Technique. However, Itachi was easily able to cut off the seven snake heads, leaving only one behind whose mouth Orochimaru appeared out of and thanked Itachi for pushing Sasuke so far, in the process setting him free and allowing him to take control of Sasuke's body. Itachi, however, stabbed Orochimaru with the Totsuka sword to seal him away with Susanoo, thereby removing the cursed seal from Sasuke's body.

Itachi's last smile to his little brother, Sasuke.

Added by AlienGamer

As Itachi began to weaken, thus weakening Susanoo, Sasuke saw an opportunity to strike, but in vain, as Susanoo was still able to protect Itachi. His last option gone, Sasuke was pushed against a wall and left helpless as Itachi walked up close to him and seemed to be reaching for Sasuke's eyes. However, he instead poked Sasuke's forehead and smiled before saying, "Forgive me Sasuke... ...It ends with this."; this was a reference to Itachi constantly poking Sasuke on the head when they were younger. With that act, Itachi finally gave in to his fatal illness, which he had been using medication and sheer willpower to fend off, and died.