Shikamaru and Sasuke have never been close, but it was Shikamaru’s part of the role to lead the campaign to bring Sasuke home. Shikamaru managed to rescue Sasuke for what reason?
Shikamaru is obligated to save Sasuke because Hokage Tsunade has sincerely asked for it. Because all of the Jonin are on the other missions, she assigns the Sasuke-retrieval mission to the newly Chunin Shikamaru. Tsunade orders him to accumulate as many Genin as he requires and to leave the village as soon as possible. She also urges Shikamaru to include Naruto in the venture to save Sasuke. Other squad leaders may not want Naruto to join them, but Shikamaru isn’t of sufficient rank to refuse Naruto. Tsunade already appears to know Naruto would indeed be disappointed if the leader of Sasuke’s retrieval mission didn’t want him.
Shikamaru is Tasked With Rescuing Sasuke:
Tsunade, the fifth Hokage, decided to invite Shikamaru to her headquarters in Chapter #182. She notifies him that Sasuke Uchiha has fled the Neighborhood and is most likely on his way to the Township Hidden in The Sound. Sasuke eventually offered to send himself to Orochimaru for the sake of authority and the advancement of the potential of his curse mark.
Tsunade claims that the mission requires prompt attention and that there will likely be complications. Orochimaru’s henchmen may assist Sasuke in traveling between lands and reaching their venue. Shikamaru appears to think to himself while the prospect of trying to retrieve Sasuke has grown tedious. “Among my peer group, he was exceptional in every way,” Shikamaru observed. “He was unquestionably superior to me.” He suggests to Tsunade a four-man team of Jonin and at least Chunin. She dismisses the idea, trying to remind Shikamaru that several of the Jonin are on other tasks.
Shikamaru believes that, while the quest is unpleasant, he cannot simply ignore it. He chooses to believe it will all work out in the end. So there you have it. Shikamaru is obligated to save Sasuke because Hokage Tsunade has genuinely requested it. All of the Jonin are on other missions, so Shikamaru is given the responsibility as the only available Chunin.