One reason could be jealousy. Maybe Nico is jealous of Percy's popularity at Camp Half - Blood. Another reason might be a difference in their goals. Percy wants to protect the camp and the mortal world in a certain way, and Nico has his own ideas that don't align with Percy's. So, this divergence of interests could lead to a fight.
A possible reason for a Percy and Nico fight in fanfiction is their different backgrounds. Percy has grown up in the mortal world for a while and then at Camp Half - Blood, with a relatively more stable support system. Nico, on the other hand, has had a more tumultuous past, losing his sister and being on his own in some ways. This difference in their experiences could lead to different worldviews. If they come into conflict over how to handle a situation, say, dealing with a new monster, their different worldviews could explode into a fight.
They could fight due to a prophecy. If there's a prophecy that involves one of them being the 'chosen one' and the others think they should be, it would create a lot of tension. For instance, if the prophecy says that only one of them can save the world from a certain doom. Percy, being the main character in many stories, might be assumed by the others to be the one, but Thalia and Nico may believe they have just as much right. Their struggle for that role could lead to a fight. And during the fight, they would use their unique abilities. Percy would call upon the water, Thalia would summon her lightning bolts, and Nico would raise the dead to fight on his behalf.
A Percy and Nico fight in fanfiction might be a complex affair. Their respective loyalties could come into play. Percy is loyal to Camp Half - Blood and Nico has his own complex allegiances. They could be fighting because of different ideas about how to deal with a new threat to the demigod world. Percy might think of a more upfront approach using his powers, while Nico could be more inclined towards using his knowledge of the Underworld and the dead to outwit the threat. This difference in approach could lead to a fight between them as they try to impose their methods on each other.
Another reason might be the stress of their quests. They are constantly under pressure to save the world or their friends. This stress can build up and cause them to lash out at each other. For instance, if a quest isn't going well and they keep hitting dead ends, they might start blaming each other for mistakes made along the way.
Well, perhaps Percy has some personality traits that don't mesh with what Nico is attracted to. Maybe Percy is too outgoing and boisterous for Nico, who might prefer someone more reserved.
Misunderstandings about their future plans often lead to fights. Percy might want to focus on one type of adventure while Annabeth has other ideas. They argue about it, but in the end, the love between them overcomes the differences and they kiss. This shows how their relationship is complex and full of different opinions that need to be resolved.
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.
In some fanfictions, it could be related to power dynamics. Percy is often seen as a powerful and popular character. If he uses his influence or power in a wrong way towards Nico, like excluding him from a group activity or mission that Nico really wanted to be part of, it can be a reason for Nico to cry.
One possible reason is that their personalities clash. Percy is often portrayed as a more outgoing and confident character, while Nico is more introverted and brooding. In a fanfic, this could lead to misunderstandings and animosity between them. For instance, Percy's bold actions might seem reckless to Nico, causing him to dislike Percy.
It might be a test of strength. They could both be trying to prove themselves, either to their friends or to some higher power in the fanfiction world. They want to see who is truly the stronger hero.
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.