Obviously, Naruto would be the main character since it's about him being the last male. But other characters like Sakura, Hinata, and Tsunade would also be important. They would play roles in either protecting Naruto or dealing with the situation his existence creates.
The main character is Naruto as it's in the title. But considering the situation, female characters such as Ino, who was Naruto's classmate, could be significant. She might be involved in trying to figure out a solution to the problem of Naruto being the last male. Also, Temari from the Sand Village could be involved as the situation would have an impact on inter - village relations too. So these female characters along with Naruto would be the main ones in this fanfiction.
In this fanfiction, Naruto is the central figure as it's about him being the last male. However, other characters will also be key. Hinata, who has always had feelings for Naruto, would be crucial. She might be at the forefront of trying to keep Naruto safe. Then there are the female ninja leaders like Mei Terumi from the Mist Village. She would be involved as the situation of a single male left in the world would have far - reaching implications for all the villages. So Naruto, Hinata, and Mei Terumi could be among the main characters in this 'Naruto the Last Male in the World' fanfiction.
Obviously Naruto would be the main character as the title implies. He is the one creating the world, so he would be at the center of the story.
In 'naruto last moments fanfiction', Naruto is the main focus, but other characters are crucial too. The other members of the Konoha 11 would probably be there. Shikamaru, being Naruto's close friend and a strategic thinker, might be devising plans to save him or at least make his last moments comfortable. Ino could be using her mind - transfer jutsu to communicate with Naruto in his last moments if he's unable to speak. Choji might be there, offering his emotional support with his kind - hearted nature. And Naruto's son, Boruto, would definitely be present, learning from his father's last moments and vowing to carry on his legacy.
Most likely, there will be trainers. They could be young and enthusiastic about Pokemon. For example, a boy trainer who has been on a long journey and finally meets his childhood friend who is also a trainer.
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.
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.
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.
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.
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.
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.
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.