In this fanfiction, perhaps Naruto, Sasuke and Sakura are recognized as the new Sannin after they complete a series of extremely difficult tasks. Naruto's role could be the one with the most raw power, Sasuke as the strategic and stealthy one, and Sakura as the one who holds the team together with her intelligence and medical support. They might encounter a mysterious old sage who tests them to see if they are truly worthy of the Sannin title.
One idea could be that they go on a mission together to a far - off land. Naruto uses his new - found Rasengan variations, Sasuke with his evolved Sharingan techniques, and Sakura with her enhanced medical and combat skills. They face a powerful enemy that was once defeated by the original Sannin and they have to use their combined skills to overcome it.