The main characters would be Naruto and Axel. But there could also be other characters from the Naruto universe like Kakashi. Kakashi might be suspicious of Naruto's new abilities and try to figure out if they are a threat or not. And from Axel's side, his friends like Roxas could also make an appearance. They might initially be hostile towards Naruto but then learn to accept him as he proves himself.
Naruto and Axel are the central figures. However, in the Naruto world, Sasuke could also play an important role. He might be intrigued by Naruto's new powers and want to either steal them or learn from Naruto how he got them. And from Axel's world, characters like Xemnas could be part of the story. Xemnas might see Naruto as a tool to achieve his own goals, and Naruto has to resist him while also trying to understand his connection to Axel.
Obviously Naruto would be one of the main characters. He's the protagonist of the original series and his power and will would be crucial in a doomsday scenario. Sasuke would also be likely, as his strength and his connection to Naruto are important elements. Sakura, with her medical skills, would also be a key character as she could be responsible for healing the injured during the doomsday chaos.
Well, it's possible that some new or less - known characters from the Naruto universe could become main characters in 'chaos naruto fanfiction'. For example, Rock Lee could take on a more central role. He has always been a character full of determination and unique fighting style. In a chaotic setting, his strong will could be a key factor in dealing with the chaos. And then there are the jinchuriki of the other tailed beasts who might be more prominently featured as they are all related to the power dynamics in the Naruto world which could be thrown into chaos.
Obviously, Naruto would be one of the main characters. Since it's a Naruto - centered fanfiction with the beyonder element added. Sasuke could also be a main character as he is often Naruto's counterpart and rival. They might both be involved in exploring the beyonder powers. Additionally, characters like Kakashi could play important roles. He could be the one guiding Naruto and Sasuke in understanding these new and strange beyonder powers, given his experience and wisdom.
There may be new characters introduced as well. Maybe a mysterious figure who has a special ability to either enhance or dampen Naruto's will to live. This character could add an extra layer of mystery and conflict to the fanfiction.
Naruto would be the central figure. But in this British version, there could be new characters added, like a British wizard - type character who becomes Naruto's mentor in understanding the new 'British - ninja' aspects of his life. And of course, Sasuke and Sakura would be adapted to fit the British setting, perhaps with different family backgrounds that are more in line with British culture.
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.