—Tennin—
#01: Fall of the Datenshi
Naruto secretly enlists into a top-secret organization called Tennin. Their sole goal is the eradication of war through armed force, carried out by the Datenshi. The plan was originally outlined by the legendary Rikudou Sennin. It was designed to unite the world under one banner so that people would stop fighting each other and find common ground so that they could live in peace, even if it meant destroying Tennin and all the Datenshi.
During his quest to become the next Juubi Jinchuuriki, Madara came across the concept of Tennin and used it as a model that he based his Akatsuki off of. However there was a significant difference between Akatsuki and Tennin: Akatsuki was designed to help Madara rule the world through the Mooneye Plan. To Madara's knowledge, Tennin was never truly founded and remained an untapped legacy of the Rikudou Sennin.
But Tennin was very much alive and active, hidden extremely deep under the surface. Many of the greatest ninja of the shinobi world had been secret members of Tennin. The Shodai and Nidaime Hokage were both members and had based Konoha off of the principles of Tennin, knowing that many other countries would follow their lead once a major power was introduced into the world.
After the Third Great Ninja War ended, Tennin began secretly marshaling its forces and enlisting high-level ninja into their ranks. When signs of another war was slowly brewing (Tobi's handiwork), such as the Kyuubi attack on Konoha, Uchiha Massacre, Bloodline Wars in Water Country, Lightning Country's continued mobilization, and Orochimaru's experiments and defection, they knew that the Fourth Ninja War wasn't far off.
Naruto and Sasuke, age 5, were prospects of Tennin because of their heritages and potential skills (Kyuubi, Sharingan). Itachi, a Datenshi of Tennin, had been assigned to discreetly training Naruto in the Ninja Arts. Naruto took to the training like a fish to water because he saw it as wrestling games and learning skills that would help him to prank people (stealth, traps, evasion, concealment, and feigning innocence). Sasuke was to be trained by Uchiha Shisui, who was Itachi's best friend, Datenshi partner, and chosen by Fugaku. When the Uchiha Massacre occurred, Itachi was unable to stop it or prevent without blowing his cover as a Datenshi, thus was forced to play along with Danzo's plans. Shisui didn't even put up a fight when Itachi had to kill him to gain the Mangekyou Sharingan.
With the Uchiha Massacre, Itachi was forced to flee Konoha. But before he left, he told Naruto to find Sasuke, leave Konoha, and journey to Wave Country where they could meet a ninja named Iyadomi Akira who could complete their training. Naruto, having grown very fond of Itachi, obeys his orders and was able to sneak Sasuke out of Konoha, enticing him with the promise of super-awesome ninja training. They are able to go several days without being noticed that they were missing thanks to key figures in Konoha being Tennin operatives. Upon reaching Wave, Naruto and Sasuke begin their training.