In addition to Naruto and his usual comrades, the bijuu themselves could be considered main characters in a sense. They have their own personalities and powers, and in a fanfiction where Naruto is the master of them, their interactions with Naruto would be crucial. For example, Kurama, the Nine - Tails, would play a significant role as Naruto's main bijuu partner. And villains who oppose Naruto's new - found power over the bijuu could also be main characters, adding conflict to the story.
Obviously Naruto is one of the main characters as the title implies his role as the master of bijuu. Other characters could include his friends like Sasuke and Sakura. Since it's related to bijuu, the jinchuriki of other bijuu might also be important characters, like Killer Bee who was the host of the Eight - Tails.
Well, Naruto is the obvious main character. However, depending on the plot, characters like Kakashi could be involved as well. He could be guiding Naruto in handling his godlike powers. And the villains in the fanfiction could also be main characters in a sense, as they would be the ones creating challenges for Naruto in his new state with the godlike bijuu powers.
In some popular 'naruto female bijuu fanfiction', characters like Hinata can often be reimagined as a female jinchuriki. Another common main character is an original female character created specifically for the fanfiction. Sometimes, Sakura is also given the role of a jinchuriki in certain fanfictions.
The bijuu are the main characters as they are the focus of the 'goes to Yuki Academy' part. However, depending on how the story unfolds, there might be some side characters like the academy's janitor who has some secret knowledge about the bijuu and ends up helping them in unexpected ways, but still, the bijuu are the central figures.
Sasuke could also be a main character. His quest for power and his unique abilities might make him interested in the artificial bijuu. He could either be trying to use them for his own goals or be against their existence, depending on the plot of the fanfiction.
Well, without actually reading it in detail, generally in such a fanfiction, Naruto might have some extraordinary adventures related to his control over the bijuu. He could be using their powers in unique ways to fight enemies, or perhaps he's on a journey to master their full potential and face new challenges that come with that power.
Maybe there's a rogue ninja who has developed a new and dangerous jutsu that can counter Naruto's powers. This ninja wants to prove himself as the strongest by defeating Naruto and taking over the bijuu's power. He might be jealous of Naruto's newfound status and the respect he gets from the other ninjas.
It could be an ancient sage. In Naruto lore, there are sages who have had a great influence on the world. An ancient sage could be the one who created or fathered the bijuu. Maybe he had some great power and knowledge that allowed him to bring the bijuu into existence.
Obviously, Naruto Uzumaki is often a main character as he is the jinchuriki of the nine - tailed fox. Gaara, the one - tailed beast's jinchuriki, is also frequently featured. And sometimes, other jinchuriki like Killer Bee, who has the eight - tailed ox - like beast, can be main characters too.
Naruto himself is often a popular character in such fanfictions. Since he has a strong connection with the bijuus, especially Kurama, his time - traveling adventures can create really interesting stories. Another popular character is Sasuke. His power and his complex relationship with Naruto can add depth to time travel plots.
It could be Shukaku. Since Shukaku was one of the first bijuu introduced in the series and has a sand - based power, it would be an interesting addition to Naruto's arsenal. Naruto's positive and energetic personality could also have an impact on Shukaku's usually grumpy and solitary nature.