One of the most interesting things about the Naruto franchise is the existence of the Tailed Beasts and their Jinchuriki. There were a total of nine tailed beasts in the Narutoverse, related essentially as siblings. However, the one-tail developed a rivalry with the nine-tails, causing them to always quarrel and try to surpass each other in everything.
Years before the birth of Shinobis, Kaguya Otsutsuki absorbed the God Tree and morphed into the Ten-Tails (Juubi). She rampaged earth in order to claim all chakras back to her but was sealed by her two sons Hamura and Hagoromo Otsutsuki. With the ten-tails extracted from her, Hagoromo (Sage of Six Paths) sealed it into himself. After the sage grew older, he used his power of Creation Of All Things to split the ten-tails into nine different tailed beasts (Bijuu); each tailed beast was named according to the number of tails it possessed, from one-tail to nine-tails.
Years later, the tailed beasts were revered as huge chakra demons and weapons of mass destruction, hence they were sealed into humans which would be known as Jinchuriki. Shukaku (one-tail) was later sealed into Gaara, while Kurama (nine-tails) was sealed into Naruto. Both had been sealed into two Jinchuriki prior to being sealed into Gaara and Naruto .
Kurama believed he was the strongest of among the tailed beasts because their powers were ranked according to the number of tails they possessed. This only caused other tailed beasts to dislike him, especially Shukaku, who has always disagreed with Kurama's headership and would frequently argue.
RELATED: Best of Frenemies: Why Do We Love Anime Rivalries More Than Anime BFFs?
Even though their rivalry started long before they were sealed into their Jinchuriki, Kurama and Shukaku shared certain attributes, most notably a hatred of humankind. Shukaku always threatened to take over the body of his Jinchuriki if they slept too much, and he would rampage the village. Kurama would do the same thing, often getting angry when his jinchuriki refused to use his chakra in battle. His intent was to overpower the Jinchuriki with his chakra and take over their body.
With much effort and convincing, Kurama and Shukaku later acknowledged their Jinchuriki and let go of their hatred. Naruto and Gaara managed to befriend both tailed beasts, and they were able to fight alongside each other as comrades. During the Fourth Shinobi World War, while Kurama gave orders to the other tailed beasts on how to fight against the ten-tails, Shukaku showed his distaste in the leadership. While the two bijuu seem to have resolved their rivalry after meeting Hagoromo following Kaguya’s defeat. After the Fourth Shinobi World War, Kurama willingly returned to Naruto’s body on Hagoromo’s request while Shukaku willingly stayed alongside Gaara, they now befriended humans.
In Boruto: Naruto Next Generation, after Kurama saw Shukaku reduced into a small size and put into a small pot for protection against Urashiki Otsutsuki, he mockingly teased Shukaku. Angry at this, the two started an argument which was abruptly ended by Naruto. Although their rivalry has subsided, it contributed greatly to the series.