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.
It could also be due to a misunderstanding. Suppose Naruto accidentally does something that Kurama misinterprets as a threat to its own existence. For example, if Naruto tries a new jutsu that Kurama wrongly perceives as an attempt to suppress it further.
Some fans are deeply moved. They might cry while reading it because Naruto has been such an important and beloved character throughout the series. His sacrifice represents the ultimate act of heroism, and fans who have grown attached to him over the years would feel a strong emotional connection to such a story.
Yes, in fanfiction, Naruto can do all sorts of things that might not be shown in the original series, like rapping. Writers often take creative liberties in fanfiction to explore different aspects of characters. So it's not unusual to find a story where Naruto has a hidden talent for rapping, perhaps to inspire his friends or as a new form of ninja art.