One key element is empathy. Naruto has to be able to empathize with Kurama's situation. Kurama has been locked away for a long time and has a lot of pent - up anger. If Naruto can understand that and show that he cares, it helps build the friendship. Another is communication. They need to be able to talk to each other, which in fanfiction often involves Naruto learning to communicate with Kurama on a deeper level than just yelling commands at his chakra.
In some fanfictions, Naruto and Kurama start to understand each other during their battles. As Naruto constantly shows his determination and never - gives - up attitude, Kurama begins to respect him. For example, when Naruto is facing a powerful enemy and still tries his best even on the verge of exhaustion, Kurama sees his tenacity and starts to have a change of heart. This is a common way for them to start building a friendship in fanfiction.
In some fanfictions, Naruto becomes friends with Kurama through deep conversations. Naruto, being persistent, tries to understand Kurama's pain and anger. He shares his own experiences of being alone and ostracized. This mutual sharing of feelings gradually breaks down the barriers between them, leading to friendship.
One idea could be that Kurama, with his powerful demon abilities, has a unique bond with psychic - type Pokemon like Alakazam. Maybe he uses his chakra control skills to communicate with them in ways normal trainers can't. He could start his Pokemon journey in a region filled with mysterious forests, similar to the ones he knew in his original world, and form a team of Pokemon that complement his own strengths.
A key moment could be when Naruto saves Kurama from some external threat. For instance, if there's a dark force trying to control Kurama, Naruto steps in and uses his own chakra to free Kurama. This act of selfless rescue makes Kurama see Naruto in a new light and starts the friendship.
If Kurama becomes Naruto's father in fanfiction, it could completely change Naruto's character development. He might inherit more of Kurama's powers directly. For example, he could have better control over the Nine - Tails' chakra from the start, without having to struggle as much as in the original story.
Well, Kurama might train Naruto by teaching him how to better control and access chakra. Since Kurama has a vast amount of chakra, it could show Naruto unique ways to harness and use it. For example, it could guide Naruto in creating more powerful and complex jutsu by using their combined chakra in a more efficient way.
Sakura might be really surprised at first. She could be a bit skeptical about whether it's really Naruto or some kind of trick. But then she would probably try to help him find a way to change back.
Since Kurama has a vast amount of knowledge and power, he could guide Naruto in ways that no one else could. Naruto could learn to transform into different forms of the Nine - Tails more easily and use that power more effectively in combat. This would make his training more focused on harnessing his in - born abilities.
Naruto's self - confidence gets a huge boost. Kurama's teachings are like a seal of approval. If Kurama believes in him enough to teach him, then Naruto must be something special. This new - found confidence shows in his posture, his speech, and how he faces challenges. He no longer doubts himself as much when it comes to difficult tasks, whether it's a tough battle or a diplomatic negotiation within the ninja world.