The fanfiction might introduce characters from Greek mythology since Helios is from Greek mythology. For instance, there could be a character like Apollo, who could either be an ally or a rival to Naruto. The nine - tailed fox inside Naruto could also have a different relationship with Naruto due to his new heritage. It could be more cooperative or even act as a source of advice regarding Naruto's new powers.
There could be antagonists specifically targeting Naruto because of his relation to Helios. They might be from a group that has a vendetta against Helios or wants to use Naruto's power for their own evil purposes. Kakashi could play an important role in guiding Naruto through the discovery of his heritage and helping him control his new powers. And there might be some sort of council in the ninja world that has to deal with the implications of Naruto being the son of a god - like figure.
Obviously Naruto himself. Then there could be new characters related to Helios' realm, like solar - powered guardians who come to protect Naruto or teach him about his heritage. Also, the existing Naruto characters would still be there. Sasuke might be intrigued or even jealous of Naruto's new powers. Sakura could be worried about how Naruto's new identity might change him.
Obviously Naruto is one of the main characters. He is usually the central figure around which the story of the fanfiction revolves. Another character could be a new character created specifically for the fanfiction who has some connection to Helios, like a guardian or a guide for Naruto in his journey related to Helios.
In this fanfiction, characters like Hagrid could also be involved. He could befriend Naruto and introduce him to the more positive aspects of the wizarding world. And of course, there could be other Death Eaters who might either try to use Naruto or see him as a threat due to his relation to Bellatrix.
Well, Naruto is the key character here. Then we could have other Naruto characters like Jiraiya. In the Olympian part, Hermes could be a character as he could be the one to guide Naruto in the Olympian world. Also, Aphrodite might be there, perhaps using her charm powers to either help or hinder Naruto. And in the Naruto world, we can't forget characters like Gaara who might react in different ways to Naruto's newfound Olympian identity.
One potential character could be Kakashi. He would probably be very confused and concerned about Naruto's situation. He might try to train Naruto to control his powers in a way that doesn't harm himself or others. Another character could be Tsunade. As the Hokage, she would have to decide how to deal with Naruto. She could either support him or try to keep him in check. And of course, there could be some villains from the Deathwing side who come to either recruit or destroy Naruto.
Obviously Naruto would be the main character. Shukaku itself or a representation of Shukaku's spirit could be there. Also, characters like Iruka sensei would still be around. His friends like Sasuke and Sakura would play important roles as they react to Naruto's new situation.
Obviously Naruto himself. Then there could be other Naruto characters like Sasuke and Sakura who would react to Naruto's new heritage. Also, characters related to Mileena might be introduced, perhaps some of her allies or enemies from her own story.
Obviously Naruto as the main character. Gabriel would be a key figure, perhaps appearing in flashbacks or even in a more present form to guide Naruto. There could also be other Naruto characters like Kakashi, who might be intrigued by Naruto's new heritage and try to help him understand and control it.
Obviously Naruto himself. There could also be characters from the Naruto universe like Kakashi, who might be involved in Naruto's discovery of his Sabertooth heritage. And perhaps some original characters related to the Sabertooth aspect could be introduced.
I think characters like Jiraiya would be important. Since he was Naruto's mentor, he could help Naruto understand and control the power related to being the son of fury. And of course, Naruto's family members, even if they are not alive in the original series, could be explored in this fanfiction, such as his father who might have passed on this 'son of fury' trait.
Obviously Naruto himself. Then there could be characters like Sasuke who might react differently to Naruto's newfound parentage. Sakura too, she might be concerned about how this affects Naruto and their team. Kakashi could also play an important role, perhaps guiding Naruto through the confusion of his identity. And who knows, some of Deidara's old Akatsuki comrades might show up to either help or harm Naruto depending on their motives.