Obviously, Percy Jackson is the central character. The Olympians such as Zeus, Poseidon, and Athena are likely to be involved as the ones doing the betraying. Other demigods like Annabeth Chase could also be part of the story. She might be torn between her loyalty to Percy and her respect for the Olympians. There could also be minor gods and goddesses who either side with Percy or the Olympians, depending on their own motives and relationships. For example, Hades might see an opportunity to gain more power if Percy is out of the picture, or he could help Percy out of a sense of fairness.
The Olympian council as a whole is involved in the sense that they either support or allow the betrayal to happen. Poseidon, Percy's father, could be in a difficult position. He might be pressured by the other Olympians to abandon Percy or he could secretly try to help his son. Chiron, the centaur trainer at Camp Half - Blood, would also play a role. He might be one of the few voices of reason, trying to convince the Olympians that Percy is being wronged, or he could be forced to stay neutral due to the power dynamics at play.
Ares could be a likely character. He's always been somewhat of a wild card in the Percy Jackson series. He might betray Percy for his own amusement or to gain more influence in Olympus. Another could be Zeus. He's often paranoid about his power and might see Percy as a threat and betray him to protect his throne.
Well, Ares could be involved. He has had his clashes with Percy in the original stories. In fanfiction, his war - like nature and desire for chaos could make him set up Percy to look like he's betrayed the community. Also, Octavian from the Roman side might be a character in such a scenario. He's power - hungry and jealous of Percy's status. He could spread false rumors or create situations that make it seem as if Percy has betrayed the Roman demigod community.
Well, obviously Naruto himself is the central character. Sasuke could be involved as he has a complex relationship with Naruto. In a crossover, if Naruto is betrayed and ends up in the Dragon Ball universe, Vegeta might be a character he interacts with. Vegeta could initially see Naruto as a weakling but later come to respect his skills. Another character could be Luffy from One Piece. If Naruto is betrayed and crosses over to the One Piece world, Luffy would likely befriend him and help him out, seeing Naruto's situation as similar to his own crewmates' struggles.
The main characters would include Percy as the leader. But we can't forget about Clarisse. She is a fierce warrior and would be an important part of the armies. Tyson, Percy's Cyclops half - brother, might also be involved, using his strength to fight. And then there are the minor gods and goddesses who could either support or oppose Percy's leadership, adding more drama to the story.
Grover could also be a major character. As Percy's best friend, he would probably be involved in trying to stop Percy if he thinks Percy has gone too far. Or, if he sees the corruption in Olympus, he may side with Percy. Grover's connection to nature means he could play an important role in the events that unfold, like using nature spirits to either protect Olympus or aid Percy depending on his stance.
Obviously, Naruto would be one of the main characters. He's the one being betrayed. From RWBY, Ruby, Weiss, Blake, and Yang are likely to be involved. They are the central characters in RWBY, and if there's a betrayal of an outsider like Naruto, they would probably play a significant role in it.
The gods, especially Zeus. He has always been a bit suspicious of Percy. In fanfiction, he could easily be written as spreading lies about Percy to the other gods and demigods, leading to everyone turning against him. Also, some new characters introduced in fanfiction might be the ones who start the chain of events that lead to Percy's all - around betrayal.
One character that could betray Percy is Thalia. She has her own issues with the gods and her place in the world. Maybe she gets jealous of Percy's growing popularity and power among the demigods. So, she decides to side with an enemy to take Percy down a notch. Additionally, some minor characters that Percy has helped in the past could be the ones to betray him. They might feel indebted to him but also resentful at the same time. An enemy could manipulate their feelings and turn them into traitors against Percy.
Even old enemies of the demigod world, who see Percy and Jason as threats, could be the antagonists. They might use deception and betrayal as a way to weaken the demigod forces, knowing that Percy and Jason are important figures among them.
The gods would be involved. Zeus, Poseidon, or any of the other gods. If they make decisions that affect Percy negatively, like sending him on a dangerous mission without proper support, he'd be angry. Also, Clarisse could be in these stories. She and Percy have had their share of conflicts in the original series, and in a fanfic, she could do something to really tick Percy off, like stealing his thunder (figuratively speaking) in a battle or competition.