In season 12, Episode 329 of Naruto: Shippuden, we finally get to see Naruto & Kurama becoming friends. Yet, the bond wasn’t made in one day or an episode.
The friendship between the two started off during the Kurama Chakra control arc.
Before this episode, Tobi, using his Rinnegan, had resurrected the Jinchurikis, sealed the tailed beasts back into them, and made them part of his Six Paths by embedding a chakra receiver in their chests.
How did Naruto and Kurama become friends?
In the previous episodes, we had seen the Four-Tailed Beast, Son Goku, controlled by Tobi, capture Naruto in its mouth. Tobi tried absorbing Son and Kurama with his Mangekyou Sharingan Kamui. Naruto uses his multi-shadow-clone jutsu to get out, but then Son tells him that the chakra receiver is embedded in his neck and asks him to get it out so that he can no longer be controlled by Tobi.
Naruto gets into the Chakra mode with Kurama’s help and tries to pull it out, while Tobi tries to entrap him with chains.
Even though in episode 329, Naruto successfully pulls out the receiver and destroys it, he finds out that it didn’t work in freeing Son from Tobi’s control. As a token of appreciation for trying to help, Son gives Naruto some of its chakra just before Tobi seals him back into the Gedo Mazo.
Tobi decides to go all out against Naruto and Killer B, the only two Jinchuriki he didn’t have, so he decides to make all the other Jinchuriki transform into the full-tailed beast mode.
Seeing the danger, Kurama offers Naruto his help, and they meld their chakra. Kurama rebukes Naruto for thanking him for his help against Madara, and this is where the most wholesome scene between the two happens.
Naruto and Kurama bond and the young shinobi acknowledges the fox as a friend, opening the Torii seal that had kept Kurama trapped inside him since his birth.
Naruto makes shadow clones and uses Kyuubi’s chakra arms to send them to each tailed beast under Tobi’s control to pull out the receivers.
Due to this, he enters a different dimension, where he has a talk with Kurama, the rest of the tailed beasts, and their Jinchuriki. This is where all of them get acquainted with each other, and the tailed beasts gift Naruto some of their chakra.
As Naruto is removing the receivers, Kurama asks the other tailed beasts if they, too, agree that Naruto is the shinobi their creator, Hagoromo the Rikkudo Sennin, had foretold. To which, they all agree.
With time, their friendship grew stronger, and they helped each other in countless difficult circumstances.