During the start of the Fourth Shinobi World War, Kurama tried instil doubt into Naruto by telling him that shouldering the hatred of an entire war was futile and reminding him of his failure to save Sasuke from revenge, but Naruto refuted with brimming confidence that regardless of the odds, he would still do something about them, before the young shinobi promised to someday resolve the fox's own hatred as well.Although reproaching him for making such a claim, Kurama nevertheless had developed a level of respect for Naruto and his determination, even noting that he was different from the humans it had previously encountered, eventually allowing Naruto to utilise the Nine-Tails Chakra Mode without consequence.Kurama then intentionally aided Naruto when the reincarnated Madara was fighting against one of Naruto's shadow clones and the Fourth Division, saying it would rather choose Naruto than be manipulated by the Uchiha again.
A relationship that shaped Naruto's character, albeit unintentionally, was with the tailed beast that was sealed within him since the day he was born, Kurama — the Nine-Tails.
Because he was the fox's jinchūriki, Naruto was treated as an outcast by most of the villagers and his peers until he was twelve years old.
Despite learning the truth of his nature during his fight with Mizuki, it was thanks to Iruka's kindness that convinced Naruto to continue trying to gain the villagers' acknowledgement.
Kurama had an intense hatred toward humans, for they had treated the fox and its tailed beast brethren nothing more than monsters worthy of fear and disdain, as well as powerful weapons to exploit, for centuries.
Ever since its sealing within Naruto, Kurama, believing that he wouldn't be any different, plotted to use the young shinobi's dependence on its power to break free from the seal.
Their relationship soon became even more antagonistic when Naruto discovered that he could potentially kill his comrades while under the fox's influence, which made him resolve to rely on his own power and find other ways to get stronger.
However, after he defeated Pain, Naruto realised that even though he had mastered Sage Mode, he could still not avoid using Kurama's power and sought Killer B, the jinchūriki of Gyūki, to learn how to control it.
With his mother and B's help, Naruto managed to best Kurama in combat, and separate and take most of its chakra.
Later on, when Obito tried to instil doubt into Naruto as an attempt to weaken his resolve, Kurama asked Naruto to switch once again long enough to reveal that it was sealed within Naruto to give the boy the strength to stop him while proclaiming itself as Naruto's friend, along with the confidence in its jinchūriki's ability to live up to the legacy Minato and Jiraiya left him.