While Naruto and Sasuke's true relationship to the Sage of the Six Paths. It turns out that the two are the reincarnated wills of the Sage's two sons, Asura and Indra. Like many other aspects of Naruto, Indra and Asura were borrowed from real-world mythology and adapted into the ninja manga's canon. However, unlike most of these adaptations, Indra and Asura are a lot different from their traditional roots.
In Naruto, Indra and Asura are the children of the Sage of the Six Paths. Indra, the older brother is credited with creating ninjutsu as it is known in the ninja world, believing power is achieved solely through the self. Unlike Indra, Asura was known to help and guide others, believing that power comes from the bonds shared with others. When Asura was chosen to be the Sage's successor, this angered Indra and started a feud that spanned multiple bloodlines and was resolved with Naruto and Sasuke.
Their story in Naruto couldn't be any different from their mythological origin. The two hail from Hindu mythology, which has not been adapted as widely as Shinto mythology has, but Hindu ideas do play a part in the series such as chakra and the Six Paths themselves. In mythology, Indra is the king of the gods and a warrior protector, whereas Asura refers to a group of demonic beings hellbent on taking out Indra and the other gods. Asuras have three faces, and four to six arms, which Naruto does reflect with the Six Paths Kyuubi state. Many Hindu stories feature the lives of different Asuras or tell tales of the war between them and Indra.
Most of the Shinto myths are adapted pretty faithfully into Naruto, but with these Hindu deities, it seems that only key themes were carried over. The main difference is that Naruto's Indra is portrayed as the villain, and vice versa with Asura. However, Indra was a lone deity and king that fought on his own, much like Sasuke. Asuras were known to be fueled by emotion, like Naruto, and the fact that they are a group of beings rather than a lone one reflects Naruto's Asura and his reliance on camaraderie. This mythological knowledge gives the links between Naruto's main characters and its inspiration more texture than fans might guess.
Many fans have their opinions about Naruto's reincarnation bloodline, but understanding the mythology behind it might change their thoughts. Indra and Asura in Naruto are completely different from their mythological counterparts, but thematically, one can see why they were chosen to represent Naruto and Sasuke.
