There could be some original characters as main characters too. For instance, a young shinobi from a small, unknown village who rises to prominence during the Third Shinobi War. This character could bring a fresh perspective and unique abilities to the story, interacting with the well - known Naruto characters and changing the course of the war in the fanfic.
Rock Lee could be an interesting main character for a Third Shinobi War fanfiction. Since he doesn't rely on ninjutsu, his unique fighting style could be a great asset during the war. We could see him face off against powerful ninjutsu users from other villages and prove that taijutsu is just as effective. Also, his unwavering determination could inspire his comrades during the dark times of the war.
Madara Uchiha might also be a main antagonist. His goals of reshaping the ninja world could be directly opposed to what Naruto is trying to achieve with his newfound 'godlike' powers. Madara would likely see Naruto as a major obstacle in his grand plan for the shinobi world.
Obviously, Naruto is one of the main characters since it's about his retired life as a shinobi. Sakura could also be a main character, perhaps she still works as a medical ninja and has a different relationship with Naruto now that he's retired. Another could be Boruto, Naruto's son, as he would be affected by his father's retired status.
Obviously, Naruto is one of the main characters as it's about him being a shinobi god. His friends like Sasuke and Sakura are likely to be important as well. They might support Naruto in his new role or have their own story arcs related to Naruto's transformation.
Sometimes, characters like Kakashi could also take on a different role in these fanfics. He might be faced with moral dilemmas that are far more complex than in the original series due to the darker nature of the story. And there could be antagonist characters that are original to the fanfic, like a powerful and evil shinobi leader who is trying to reshape the ninja world according to his dark vision.
Most likely Naruto himself could be one of the main characters as he has always been associated with the idea of peace in the Naruto series. He might be leading the efforts to bring about a more peaceful ninja world.
Obviously Naruto would be one of the main characters as the title implies he's the 'god of shinobi'. Sasuke could also be a main character as he has a long - standing relationship with Naruto in the original Naruto story. Sakura might be in it too, since she was part of Team 7 with Naruto and Sasuke.
It could also be a veteran ninja who has already seen a lot in their life but is still drawn into the Third Shinobi War. This character could have a complex backstory, perhaps they lost someone dear in a previous war and are now fighting to prevent the same from happening to others. Their wisdom and experience could be a key factor in the story.
Another possible plotline is the strategic battles. The fanfic might detail how different ninja villages coordinated their forces, planned their attacks, and countered the enemy's strategies. It could also explore how alliances were formed and broken during the intense conflict of the Third Shinobi War.
It could be an original character created specifically for the fanfic. This character could be a young ninja with a unique power or backstory, like a shinobi who has the ability to control plants in combat.