Another reason could be different loyalties. Thalia has her own group of friends and allies, and Percy has his. There could be a situation where their friends' actions or needs put them at odds with each other. For example, if Percy's friends get into trouble with something related to Thalia's friends' territory or interests, it could spark 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.
One possible reason could be that she has a deep emotional bond with Percy. Maybe they've been through a lot together, and she's afraid of losing him. So she becomes possessive to ensure he stays by her side.
In the fanfic, it could be that Percy and Thalia have a certain level of trust and understanding that Jason lacks with either of them. For example, they might communicate in a way that Jason wishes he could with them. Percy's relationship with the gods, especially Poseidon, and Thalia's connection to Zeus might make them a more formidable and enviable pair in Jason's eyes. He may be jealous of the power dynamics and the way they interact within the story.
In a fanfic about Percy and Thalia's fight, it could start because of a misunderstanding. Maybe Thalia thinks Percy is getting too much attention from the gods and she's jealous for the sake of all the half - bloods. Percy, on the other hand, might not understand why Thalia is so hostile all of a sudden.
Another reason could be that Harry has other priorities in the fanfic. He may be more focused on solving a mystery, helping a friend, or achieving a personal goal that doesn't involve fighting. So, fighting is not on his agenda.
Well, it could be about a misunderstanding. Maybe Percy accidentally uses his powers in a way that Thalia misinterprets as a threat to her leadership among the demigods. So she lashes out at him, and Percy, not one to back down easily, fights back.
They could be like siblings. Percy and Thalia might act as the older siblings, protecting and guiding Nico. Percy, with his leadership skills, and Thalia, with her combat abilities, would be great at looking out for the younger Nico. They could also be like cousins, with a close - knit bond but still having their own individual family heritages that sometimes create interesting dynamics.
One possible reason could be that Percy has unspoken feelings for Annabeth. He might be in love with her but not yet ready to admit it, so he just stares, trying to figure out his emotions.
Well, it could be about different understandings of Percy. Annabeth knows Percy as a demigod, as a hero in their world. Rachel, on the other hand, might see Percy in a different light, more as an individual outside of the demigod stuff. They might fight because they both think they know what's best for Percy and how he should be. Also, it could be a fight for Percy's future. Annabeth might want Percy to stay in the demigod world and continue their adventures together, while Rachel could have different plans for him.
One reason could be jealousy. Maybe in the fanfic, Annabeth gets more attention or praise for her skills and Percy feels left out or overshadowed, which turns into hatred. Another possibility is that there's a rift caused by their different approaches to solving problems. If Annabeth's logical thinking clashes too much with Percy's more instinctive ways, it could lead to resentment.