One possible reason could be jealousy among other characters. Maybe there are those who envy Percy's powers and leadership, Jason's status as a hero, or Nico's unique abilities. Another reason might be a misunderstanding. For example, they could be wrongly accused of a crime they didn't commit, which leads to others turning against them.
Well, in fanfiction, it could be part of a grand scheme by a villain. The villain might manipulate people into believing that Percy, Jason and Nico are threats. They could spread false rumors about them, like they are secretly working for an enemy. This would cause their friends and allies to feel betrayed and turn against them.
Well, they could be betrayed by someone they trusted deeply, like a fellow demigod. Maybe this person spreads false rumors about them, leading to their isolation within the demigod community. The three of them would then have to struggle to clear their names and find out who really set them up.
One possible reason could be jealousy among his peers. Maybe someone was envious of Percy's skills or popularity and spread false rumors about him, leading to his betrayal. For example, if Percy had a special power or was favored by a certain group, others might feel left out and decide to turn against him.
One possible reason could be that his friends wrongly accused him of something major. For example, if they thought he was secretly working for an enemy and didn't give him a chance to explain. Another reason might be that the gods themselves turned against him unjustly, perhaps because they feared his growing power and influence. This could make Percy feel so alone and betrayed that he decides to join Chaos as a form of revenge or to find a new place where he is accepted for who he is.
Well, it could be because they both care deeply about Nico in different ways. Maybe Jason sees Nico as a great friend and ally, and Percy feels the same but in a more possessive way. In fanfiction, authors often play with these complex relationships to create drama.
In many Percy, Nico, and Jason - related fanfictions, the idea of betrayal can vary greatly. It could be that in some stories Jason betrays Percy out of loyalty to a different group or a misunderstanding. For example, if there's a power struggle within a camp and Jason believes Percy's actions might endanger the whole camp, he might take actions that Percy perceives as betrayal. However, it could also be Nico who is betrayed by the other two if they accidentally expose his secrets that he's been keeping to protect himself and others.
The camp leaders might betray them. If there is a power struggle within the camp, and Percy and Nico are seen as threats to the current leadership's power, the leaders could set them up. They could make it look like Percy and Nico are breaking camp rules or endangering the other campers, which would lead to the rest of the camp turning against them.
Sometimes, the betrayal in fanfiction is based on a prophecy or a pre - determined fate. Say, there's a prophecy that one of them will betray the others to save the world. Jason might be the one who is fated to do this. He battles with this knowledge internally, and when he finally does the 'betraying' act, it's a very emotional and complex moment. Percy and Nico are shocked and hurt, but then they have to figure out if they can still work together to face the greater threat.
In a 'Percy and Nico are betrayed' fanfiction, perhaps they are betrayed by the gods. The gods, fearing their growing power, might spread lies about them among the demigods. Percy and Nico then have to fight not only against the false accusations but also the demigods who turn on them. They would have to find a way to clear their names and prove their loyalty.
Percy might be angry at first. He's used to being a loyal friend, so betrayal would hit him hard. He'd probably try to find out the truth and clear his name. Jason, being a more diplomatic type, might initially be shocked and then try to reason with those who betrayed him. Nico, on the other hand, could retreat into himself. He has a more solitary nature, and the betrayal might make him even more withdrawn.
It could be a jealous demigod. Maybe someone who is envious of Percy's popularity and Nico's unique powers. This person might see an opportunity to get rid of them and take their place in the demigod hierarchy.