While everyone is getting on with their everyday lives, Sasuke is still in the hospital recovering from his battle with Aoi. He is tormented by the comments and taunts of their past enemies about his having been the only survivor of the Uchiha clan (we this is not true, since we've already seen Itachi alive) and his actually being the weakest.
He seems particularly intent on punishing himself for having lost the battle and continues recalling things from the past. This time he remembers Itachi's words "Right now, You don't interest me" while at the same time remembering Jiraiya's comment that Itachi's "target was Naruto after all". He seems to be angered by this, but is interrupted by the arrival of Naruto and Sakura, who wonders where the knife she was going to use to core Sasuke's (she has been babying him apparently) apples went.
He once again starts to recall their battles and is particularly focused on Naruto's vast improvement and apparently new repertoire of skills. We get to see a scene where Sakura is thanking him for having saved her from Gaara, but is in turn informed that it was Naruto who saved her. He comes back to himself in the hospital room and lashes out against Sakura who was at the time passing him an apple, prompting Naruto to get off the floor (Sakura apparently laid him out for being particularly annoying) and question what's going on.
Sasuke purposefully picks a fight with Naruto (which as we know can be quite easy to do) whom we know will not back down from a challenge. He accepts to fight and admits he's been wanting to fight him as well. Sakura is not too pleased with the idea and tries to discourage them, but is ignored by both. Naruto follows Sasuke to the hospital roof, where he's surprised to find out his "skin is actually tightening" with anticipation and excitement.
Although Sasuke started this fight, I believe it to be more important to Naruto than it is to him. This is the moment Naruto has been awaiting for so long. They purposefully psych one another up and start the fight, which seems to be pretty even until Sasuke warns him to stop messing around and steps things up a notch.
They both quickly realize this has become a real battle and begin to take out the big guns (metaphorically speaking anyways). Naruto uses his Shadow replication and completely surrounds Sasuke. He in turn has to use his Katon: Goukakyuu no Jutsu (Fire Grand Fireball Jutsu) to finish of the replicas who are fast overwhelming him.
To his dismay, Naruto and one last replica are left standing in the middle of the fireball molding the chakra for Rasengan (we can see the tendrils of the Rasengan protect him and his replica as they mold the chakra). He doesn't know what it is, but recognizes that it is very powerful and decides he needs to use Chidori against it. Sakura, who's been watching from the sidelines, tries to stop them by jumping in the middle. They both realize that they've got too much momentum and can't stop their attacks. It seems that hitting Sakura is inevitable.