In a 'naruto spirit bomb fanfic', Naruto is the central figure. However, Kakashi could be a key character too. He might be the one to guide Naruto in understanding the concept behind the spirit bomb - like power. Also, characters from the Akatsuki like Itachi or Pain could be antagonists. Itachi might be interested in Naruto's new power for some mysterious reason, and Pain could see it as a threat to his plans for the ninja world.
Obviously Naruto would be the main character as it's a Naruto - related fanfic. But other characters like Sasuke could also be important. Sasuke might be initially skeptical of Naruto's new spirit bomb - like ability or could even be jealous. Sakura could play a role in helping Naruto master this new power, maybe by using her medical ninjutsu to keep Naruto in top shape during his training.
The main characters would be Naruto and Erza. Naruto is known for his rasengan and his ability to make friends. Erza is famous for her various armors and her leadership in Fairy Tail. In this fanfic, their spirits interact, so they are the central focus. There might also be some side characters from their respective universes like Sasuke from Naruto's world or Gray from Erza's world who could play supporting roles.
Well, obviously Naruto himself would be the main character. There could also be his friends like Sasuke and Sakura, who might be involved in the interactions between the two Narutos. Maybe they are confused at first by seeing two Narutos, but then they help them figure out what's going on.
It could still be Naruto himself. Since he's the central character in the original series, many fanfics would likely continue to build on his story.
A 'naruto spirit bomb fanfic' could be centered around the spirit bomb concept borrowed from Dragon Ball. In Naruto's world, it might be a fan - created story where Naruto discovers a new power that is similar to the spirit bomb. This could be due to some sort of cross - dimensional event or an ancient power that was hidden in the Naruto universe all along. It might also be a way to bring together different ninja clans to contribute their energy to create a super - powerful attack.
Obviously, Naruto would be one of the main characters as the story is about him being the son of Whitebeard. Whitebeard himself would also be a major character, even if he might not be around for the whole story. And then there would be the other members of the Whitebeard pirates, like Marco. They would play important roles in Naruto's life in the pirate world, either as mentors or comrades.
Obviously, Naruto and Jiraiya are the main characters. They are the focus of the 'naruto meets jiraiya' concept. Naruto, the energetic and determined ninja, and Jiraiya, the wise and powerful mentor.
Naruto is surely going to be one of the main characters. After all, it's a Naruto fanfic. Sasuke is also very likely to be there as his rival and friend. Sakura might also play an important role.
Naruto himself would probably be one of the main characters. Since he has always been about protecting his friends and the village, a 'greater good' narrative could put him in situations where he has to make even more difficult decisions regarding the well - being of everyone. He might have to sacrifice his own desires for the greater good.
Sasuke could also be a main character in the 'naruto jonin exams fanfic'. His skills and his rivalry with Naruto would make for an interesting plotline during the exams. Also, Sakura might be a main character as well. She has grown as a ninja and could show off her new abilities during the jonin exams.
From the Tsukune side, Tsukune would be there as the character being bashed. His friends from his own story might also make an appearance, but mainly to be overshadowed by the Naruto characters. For example, Moka could be in it, but the focus would be on how Naruto characters are better in various aspects compared to her and Tsukune.