Since it's a Naruto - based fanfiction, Naruto himself would likely be a main character. There may also be other characters from the original Naruto series like Sasuke, Sakura, or Kakashi who could be involved in his journey as a dark sage.
Well, Naruto is surely a main character in 'naruto the dark sage fanfiction'. But other important characters could be antagonists who are trying to either stop Naruto's transformation into a dark sage or take advantage of his new state. And his friends from the original series might also play crucial roles. They could be trying to bring him back to the light or having to fight against him if he goes too far. For example, Sasuke might have a complex relationship with Naruto in this fanfiction, either helping him or opposing him depending on the plot.
Most likely Naruto would be the main character since it's about his final sage form.
Well, Naruto is likely to be one of the main characters. Since it's a Naruto - related fanfiction, he's usually at the center of the story. And of course, the phoenix sage would be another main character, whether it's an old, wise figure who imparts knowledge to Naruto or a more mysterious and powerful being that Naruto has to interact with.
There could also be new characters introduced specifically for this fanfiction. These characters might be related to the ancient sages or have some unique connection to the concept of eternal sagehood. They could bring fresh perspectives and storylines to the fanfiction.
Naruto is surely one of the main characters since it's about his reincarnation. And there would likely be his friends like Sasuke and Sakura. Also, characters related to the Sage of Six Paths might play important roles, either as allies or antagonists.
Obviously Naruto is likely to be a main character. In Naruto Hydra Sage fanfiction, there could also be an original character who is the Hydra Sage. This character might be a mentor to Naruto, guiding him in the ways of the Hydra Sage powers.
Since it's about the 'legacy of the dark sage novel', there could be a young apprentice who was once under the dark sage. This character might be conflicted about whether to follow the dark sage's path or break away from it. There could also be a wise old wizard who has knowledge about the dark sage and tries to guide others in dealing with his legacy. Another possible main character could be a brave knight who is tasked with destroying any evil remnants of the dark sage's works.
Naruto is usually one of the main characters. After all, it's related to the Naruto universe. He often has a central role, with his godlike sage abilities being the focus of the story.
The sages like Jiraiya are popular. Fanfictions might bring him back in some way to continue guiding Naruto in his sage journey. Also, characters like Fukasaku and Shima, the toad sages, are often included as they play important roles in Naruto's development of sage mode.
There could also be some original characters created specifically for this fanfiction. For example, a powerful ninja who has knowledge about the merge process and tries to either help or hinder Naruto. Or perhaps an ancient spirit that was somehow involved in the creation of Dark Naruto in the first place and now has an interest in the merge.
Sometimes other characters like Tsunade can be involved. She has a long - standing relationship with Jiraiya. In fanfiction, her presence can add a lot of drama, especially when it comes to her reactions to Jiraiya's pervy antics.