Obviously, Naruto is the main character as the story focuses on his growth of the nine tails. Kakashi could also be an important character. He might be the one guiding Naruto in controlling his new power, given his experience and knowledge. Sakura could play a role too, perhaps as a healer in case Naruto gets injured during his power - growth process.
The main characters would surely include Naruto. Another could be Tsunade. She, as the Hokage, has to manage the situation regarding Naruto's growth of the nine tails. She might be worried about the village's safety as well as Naruto's well - being. Shikamaru, with his intelligence, could also be involved, maybe coming up with strategies to help Naruto control his power and deal with any potential threats that come with the growth of the nine tails.
In addition to Naruto, the nine - tails itself can be considered a character in a sense. It has its own will and desires. Jiraiya might also be a significant character. He could have left some knowledge or training methods for Naruto to deal with the growing nine tails before his death. And then there's Sasuke. His actions and reactions to Naruto's growth of the nine tails can be a major part of the story.
Obviously, Naruto himself would be the main character. Since it's about him growing tails, he's at the center of it all. The Nine - Tails would also play a crucial role. It's the source of his tail growth. And his friends like Sasuke and Sakura are likely to be important too. They'll probably be involved in Naruto's journey and how he deals with his new situation.
Sometimes, other characters from the Naruto universe might also play important roles in these fanfictions. For example, Kakashi could be involved as Naruto's mentor, giving advice on how to better communicate with the Nine - Tails. Or Sakura might be there to support Naruto in his journey of befriending the Nine - Tails, even if she doesn't directly interact with the tailed beast.
Well, the Nine - Tails itself can be considered a popular 'character' in this type of fanfiction. It has its own personality and power, and many stories revolve around Naruto's interaction with it. Another character that might be popular is Gaara. Since he also has a tailed beast within him, there could be interesting interactions between him and Naruto regarding their respective tailed beasts, especially when it comes to the Nine - Tails.
One possible plotline could be Naruto's struggle to control the new power of the nine tails as it grows. He might face challenges from both within, like dealing with the increased aggression and power surges, and from without, such as enemies who are more afraid of his growing strength and target him more aggressively.
One possible reason could be some kind of strange chakra infusion. Maybe he comes into contact with a powerful and mysterious chakra source that mutates his body in a way that causes tails to grow. Another reason might be related to some ancient curse or prophecy. It could also be the result of a new jutsu he attempts that goes wrong and has unforeseen physical consequences.
Obviously Naruto and the Nine Tails themselves are extremely popular. Naruto is the main character of the original series and his relationship with the Nine Tails is central to the fanfiction. But other characters like Kakashi can also be popular in these fanfictions. Since he is Naruto's teacher, he might be involved in training Naruto when the Nine Tails' influence is changing Naruto's abilities. Also, Sasuke can be a popular character. His rivalry with Naruto can take on new dimensions in Naruto x Nine Tails fanfiction, especially if the Nine Tails' power gives Naruto an edge that Sasuke wants to equal or surpass.
"Naruto Geniuses Naruto" is a light novel written by the author, Wen Kunlun. It's a doujinshi derivative novel. The general plot of this novel is as follows: A fan of Naruto had transmigrated to the world of Naruto and became the protagonist, Naruto. The genius protagonist who was familiar with Naruto's plot had embarked on an unusual path. Xiao? Five hidden? What was this? The use of ninjutsu could be ever-changing, and there was no end to the development of ninjutsu. The most important thing was talent and hard work! ---------------------------- "Naruto Uzuzumaki who doesn't want to cause trouble" was a light novel written by the author, Biliao Mengyue. It was a humorous and sarcastic novel. The general plot of this novel was: The new book,"The Hero's Journey," welcomes all new and old readers to read about the world. The purpose of transmigration and rebirth was to cause trouble, but for Uzumaki Naruto, who had obtained the memories of a transmigrator, a stable daily life was the king. Hatred? Peace? War? Can everyone not be so chuunibyou? Although he did not like to cause trouble, Uzumaki Naruto decided to change the future! "I was here first!" Why should I give Sakura to Sasuke?" Hatata: "It's clear that I will be with Naruto in the future. What do you coquettish people want?!" A transmigrator failed to transmigrate, causing the Naruto World to move in another direction. ---------------------------- "Naruto no Naruto: Rebirth" was a light novel written by Bu Shi. The general plot of the novel was: The seventh generation Naruto opened the Book of Seals once again, but unexpectedly returned to his youth. Would the story of this life continue to be the same as before? Those respectable people, Bai, Third Generation Eye, lecherous immortal, ferret…can they escape the fate of death? ---------------------------- The Naruto Demon Support System was a light novel written by the author, Sheng Xing. It was an original fantasy novel. The general plot of this novel was: He had been reborn in the world of Naruto and had a system that was like a cheat. However, he had to help someone achieve great things. He would rather help his family than help reason. Therefore, he decided to help his brother-in-law, Whirlpool Naruto, save the world. He would let him become Lord Naruto, and he would be Naruto's brother-in-law! ---------------------------- "Through Naruto: I'm actually Hatsunada" was a light novel written by the author Hatsunada. It was a humorous and dissing novel. The general plot of this novel was: There were thousands of transmigrators, but he didn't expect that he could transmigrate just by doing a survey. Fortunately, all the answers in the previous survey were good, so there was not much of a problem…However, he did not expect the gender to change! Even so, it couldn't stop the protagonist from digging his way up! Orochimaru: This guy is a better scientist than me. Naruto II: She developed ninjutsu as much as I did. Sasuke: We're both cheaters, but why is she so strong? Naruto thought,'It's better to be an honest underling…' ---------------------------- Naruto: The Strongest Fusion was a light novel by the author Nian Sixteen. The general plot of the novel was: After transmigrating to the Naruto World, not only did he become Naruto, but he also had the power of fusion. The fusion of two types of chakra nature changes was called the limit of blood inheritance, and the third type was called the elimination of blood inheritance, but what about the fourth type? Five? What if he still had the Yin-Yang Escape and natural energy? Big cylinder wood Bright Night, and the enemy hiding behind her… Naruto only wanted to say,"It doesn't matter if the five words come from the sky." It was just a reasonable imagination based on the original work. There was no system, no magic, no cultivation… ---------------------------- "Naruto: Defying the Heavens and Changing Fate" was a light novel by author Zhou Julan, a derivative doujinshi novel. The general plot of this novel was: For unknown reasons, Naruto's loyal fans who retained all their memories had transmigrated to the Naruto world and became Naruto Uzuzumaki, the son of prophecy who could bring change to the world. When he was young, he met and accepted the tragedy that had not been exterminated. After Uchiha Sasuke's personality was distorted, Naruto resolutely changed his initial idea of moving steadily and following the original historical development track! With the help and support of the Nine-Tailed Demon Fox and the Nine Lamas, who had already completely trusted each other in their bodies, they destroyed the group, subdued Orochimaru, and fought against the Xiao organization…They became enemies with fate, just to break the fate of death for their companions! Welcome to group 1, group number: 307685821. ---------------------------- "Female Ninja Uzuzumaki Naruto" was a light novel written by the author in the Southwestern Border. It was a doujinshi derivative novel. The general plot of the novel was as follows: When he was 32 years old, he became the seventh generation Hokage as an unmarried bachelor. On the second day after he took over, he was directly reborn back to the year he was three years old. Naruto: "Inexplicably changed gender? That was not the main point! I'm thirty-two years old and still unmarried. I don't care about such a small matter at all! At most, I'll continue to be single." "The main point is that at this time, Ning Ci's father has not died, I Ailuo's personality has not been distorted, the Uchiha clan has not gone extinct, and Kakashi-sensei has not walked out of the shadow brought by the death of his family and friends…There are so many things that haven't been resolved yet. Is my gender still worth caring about?" * Author 698 is a fan of Zuo Ming. I don't slander anyone in the original work. If you wanted to see hot-blooded and gorgeous fights, there was no such thing here. If you had such a need, you could start with your original work. The game was late, and Lord Ban's appearance was almost over. The setting of this article is: In the seventh generation before Naruto's rebirth, Sakura, Hatata, Sasuke, and Naruto are all unmarried. After rebirth, the ending was Zuo Ming. * If you think it's ugly, just cross it and don't leave a single word. If you don't spend money, don't talk nonsense. The author doesn't owe you anything. KY is looking for scolding, 10 times the rebound, and 100% free blacklist service! ---------------------------- Naruto: The Beginning of Saiyan Bloodline was a light novel by Master Lian, a derivative doujinshi novel. The general plot of the novel was: He had transmigrated to Naruto Crown Prince, and now he was a different Naruto! "Ninth llama, let's play ~" The nine-tailed fox trembled."You…don't come over!" Naruto: "I'm just teasing you. Lend me the chakra. I'll return it to you when I'm done." Naruto hovered above the leaf. A blue ball of light slowly condensed in his hand and he threw it at the leaf below. The tyrannical energy swept out wantonly, destroying everything in its path! The world was quiet and peaceful! "I did what you said and became the one you hoped for. Demonic Fox? Plague, monsters…" No, Obito, I'm only interested in breaking the big cylinder wood. "Big cylinder wood?" What's that?" Naruto: "Bagaya Road!" ---------------------------- Naruto: The Strongest Dominator was a light novel written by the author, a derivative doujinshi novel. The general plot of the novel was: He had transmigrated to the Naruto World and became one of the three major families of the Koba family. His eyes had changed and he had gained the ability to look into his own body. He had the ability to control everything in his body while looking into his own body. He had accidentally discovered the secret of his ancestor and had embarked on a different path from the Six Paths Immortal. His new book,"From the beginning of treating Naruto's illness," had been uploaded! If you like it, you can pay attention to it...
Maybe through new jutsu or abilities. The fanfiction could give Naruto some unique power that allows him to communicate or negotiate with the Nine - Tails on a different level. He could use this power to show the Nine - Tails a different perspective, like the potential for harmony between them instead of constant struggle.
A character who is a descendant of an ancient clan that once had a connection to the Nine - Tails could be added. This character could have some knowledge about the Nine - Tails that was lost over time and could help Naruto better understand his power.
Yes, in some fanfictions, Naruto is often depicted as having a very special connection to the Nine - Tails that goes beyond the normal relationship in the original story. For example, he might be able to fully control the Nine - Tails' power in ways not shown in the canon, or they could have a mental bond that allows for unique forms of communication and cooperation.