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.
Naruto himself could be a main character as the fanfic might explore how his life could have been different without the Sandaime's influence. Another likely main character could be Orochimaru, especially if the fanfic focuses on the Sandaime's failure to deal with him properly.
Well, obviously Percy Jackson and Jason are the main ones. Given that it's a bashing fanfic, they will be at the center of the story. Their actions, personalities, and relationships will be the focus.
Well, characters who had a rough start in the village due to Sandaime's decisions might be likely to support the bashing. For example, Naruto himself could be one. Given his difficult childhood with little support from the village at first, which some might blame on Sandaime, he could be portrayed as having negative feelings towards him in these fanfictions.
One common theme could be power dynamics. Maybe in these fanfics, characters from Naruto are shown to have more power compared to Tsukune. For example, Naruto's ninja abilities might overshadow Tsukune's skills.
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.
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.