Definitely Naruto, as he is always at the center of things in the Naruto universe. His growth and development in terms of power are key aspects of the series. Then there's Hashirama Senju. He was known for his great power and his role in founding the Hidden Leaf Village. In a fanfiction about power of dominance, his power and influence could be explored further. And Kakashi Hatake could also be a main character. His Sharingan and his skills as a ninja could play a role in a story about power, especially if he is involved in a power struggle or trying to prevent someone from becoming too dominant.
Naruto is very likely to be one of the main characters. Since he is the protagonist of the original series, in a fanfiction about power of dominance, he could be the one to obtain or face this powerful force. Sasuke is also a strong candidate as he is Naruto's rival and has his own pursuit of power. Another possibility is Madara Uchiha. His powerful abilities and his desire for control in the original story make him a prime candidate for a fanfiction dealing with power of dominance.
Naruto would probably be a central character. Given that he is the protagonist of the original series, in a fanfiction about the power of darkness, his reaction to this new and dangerous power would be crucial. Sasuke is also likely to be involved. His own struggle with power and his complex relationship with Naruto could be further explored in the context of the power of darkness. Kakashi, as a mentor figure, might play a role in guiding or trying to prevent the younger characters from being consumed by the power of darkness.
In a 'naruto power of dominance fanfiction', it may focus on the evolution of power in the Naruto world. It could be that a previously unknown power source is discovered and a character harnesses it, leading to their dominance. This power could change the balance of power between the villages. For instance, if a character from a small, weak village gains this power of dominance, it could lead to that village rising in status. It might also deal with how other characters react to this newfound power, whether they fear it, envy it, or try to steal it for themselves.
Definitely Naruto himself. He'd be a central character, causing chaos and bringing energy to the daycare. And Sasuke would also be there, probably being a bit of an aloof kid that Naruto is determined to get close to.
I think Kakashi would be an important character too. He could be Naruto's mentor in this new situation, teaching him how to use his remaining abilities effectively. Also, Sakura might be there, using her medical ninjutsu skills to try and help Naruto with his crippled state.
The main characters would surely include Naruto himself. His child or children are bound to be in the spotlight. In addition, any of the Akatsuki members who may have reformed or are still causing trouble could be part of the story. For example, if Naruto's child has some connection to the Akatsuki's past actions or secrets, it could bring them into the plot. Also, the villagers of Konoha, who would interact with Naruto's family, could be important characters in this fanfiction.
Besides Naruto and Sasuke, Sakura could also be a main character in such fanfiction. Her medical ninjutsu skills might be needed to heal the wounded during the battles against Galactus. And there could be some original characters created specifically for the fanfiction who have some special knowledge or power related to Galactus and the Naruto world.
Other Naruto characters like Sasuke or Sakura might also be important. Sasuke could be involved in Naruto's new role as a 'guardian' either as a supporter or a skeptic. Sakura, with her medical skills, could play a role in helping Naruto in his 'guardian' - related adventures, perhaps by healing those affected by new threats that come with the combination of the two universes.
Obviously Naruto and Ophis. Naruto is the main protagonist from the Naruto series, and Ophis is from another fictional context. There could also be some of Naruto's friends like Sasuke or Sakura who might be involved in some way. Maybe they are worried about Naruto when he disappears into Ophis' world.
There could be new characters introduced in this fanfiction. Maybe a mysterious ninja from a far - off land who knows about Naruto's secret and either helps or hinders him. Another possibility is that an old, forgotten character from the Naruto universe is brought back and has some connection to the secret.
There could also be new characters introduced. Maybe a business rival who is jealous of Naruto's success. This rival could be from another village or even an outsider who has his own motives for trying to take down Naruto's billion - dollar empire. And of course, the Hokage would still play a role, as Naruto's actions as a billionaire would have an impact on the village's politics and power structure.