Kurama might become angry at first. He's a powerful being and being neglected would likely wound his pride. He could start causing some minor disruptions inside Naruto, like making it harder for Naruto to access his chakra.
Kurama might be a bit confused at first. A baby is not what he expected to see. He could be less aggressive than when Naruto is older. Maybe he'd just watch the baby Naruto curiously.
Kurama might be surprised. Since Naruto is just a toddler, Kurama may not expect such a small and seemingly harmless being to be his future host. He could be a bit more gentle in his initial reaction compared to when he first met older Naruto.
The characters' reactions would be complex. For instance, Iruka Sensei, who was like a father figure to Naruto, would be inconsolable. He has watched Naruto grow from a troublemaker to a hero, and this sacrifice would be too much to bear. Shikamaru, being Naruto's friend, would feel a mix of admiration and sadness. Admiration for Naruto's selfless act but sad that he's gone. The kids in the village who looked up to Naruto would be inspired in a way. They would want to be like Naruto and protect the things they love, even if it means sacrificing themselves.
His friends' reactions could vary greatly. For example, Choji might be a bit scared at first, seeing Naruto as a wolf. But once he realizes it's still Naruto, he would offer him food. Ino could use her mind - transfer jutsu to communicate with Naruto in his wolf form. And Hinata would be very concerned and would stay close to Naruto, trying to protect him from any harm that might come his way because of his new form.
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.
If Naruto were trained by the Hokages in fanfiction, it would be a game - changer. First, his chakra control would improve significantly as they are all masters in that aspect. Second, he'd inherit their wisdom. He might not make some of the stupid mistakes he did in the original story. Third, his reputation would skyrocket even more. People would see him as not just a strong ninja, but one with the blessings and teachings of the greatest Hokages. This would also have an impact on his relationships. His friends might look at him in a different light, with a mix of awe and pride.
In this 'all hokages meet fanfiction', there could be epic battles of different jutsu. Maybe the first Hokage would show his amazing wood - style jutsu to the later generations. And they might discuss how to better protect the Hidden Leaf Village from new threats.
Well, it could start with Naruto accidentally stumbling upon an ancient artifact that has the power to revive the Hokages. Once revived, they find that the ninja world is facing a new danger that is slowly corrupting the chakra of all ninjas. The Hokages then decide to train Naruto and the new generation of ninjas in a special way to combat this threat. They share their unique experiences and skills, and together they form a plan to save the ninja world from this new catastrophe.
For Naruto, it would be a whole new experience. He'd be constantly trying to communicate with the mecha Kurama, learning its quirks. Shikamaru might be the one thinking about the strategic uses of mecha Kurama in battle. He'd be coming up with plans on how to best utilize it. As for Kurama, he could be in an internal struggle. Part of him would want to stay relevant in Naruto's battles, while another part would be curious about this new mechanical version of himself and how it could help Naruto in the long run.