Well, it could be that there's some sort of magic or illusion at play. Jason might be seeing Percy as a god because he's been influenced by an external force. This external force could be an enemy trying to create chaos by making the other demigods believe Percy is a god. And Percy has to then figure out what's going on and clear his name while also dealing with the new - found respect or fear from his peers.
Some characters might be in awe of Percy. For example, Annabeth could be both proud and a little bit worried. Proud because Percy has reached what seems like a new level of power, but worried about how this new status will change him and their relationship. Grover, on the other hand, would probably be very excited. He's always been Percy's loyal friend and seeing Percy as a god - like figure would make him feel even more special to be associated with Percy.
One possible plot twist could be that Percy is initially oblivious to Jason's feelings. Then, just when Jason is about to give up, Percy discovers his own hidden feelings for Jason. Another twist could be that there's some external force, like a god or a prophecy, that tries to keep them apart. Or perhaps Jason discovers that Percy has a pre - existing relationship that he didn't know about, which complicates his crush.
Well, it could be about a misunderstanding. Maybe there's a rumor that Percy has done something bad to Jason's friends, so Jason challenges him to a fight. Percy, being Percy, doesn't back down and they start fighting. In the end, they realize it was all a big misunderstanding when the real culprit is found.
One plot twist could be that Percy's fire powers are not a gift but a curse from an enemy god. He has to figure out how to get rid of them or control them without falling into the enemy's trap. Another could be that the other gods don't accept him as the God of Fire and try to strip him of his new powers. Or maybe Percy discovers that his fire powers are linked to an ancient prophecy that he has to fulfill, and it's not as straightforward as it seems.
The plot might involve Percy and Jason having to adapt to the new and chaotic rules of the Chaos realm. They could discover new powers within themselves as they are exposed to the wild and unpredictable energy there. They might also meet old enemies who have also found their way into this strange new world, leading to some epic battles and unexpected alliances.
Perhaps in the fanfiction, Percy is under some sort of dark influence. This could be from a new, unknown magical force. This influence makes him see Jason as a threat to his friends or himself, so he attacks Jason. Jason, on the other hand, is initially confused but then tries to fight back to defend himself while also trying to figure out what's wrong with Percy.
One possible plot could be that Jason is really shy about his crush at first. He tries to be around Percy more often, like joining the same quests or training sessions. He might secretly do nice things for Percy, like leaving his favorite food at his cabin without saying who it's from.
One possible plot idea could be that Piper struggles with her feelings. She might try to deny them at first because Percy is in a relationship or because of loyalty to her friends. Another idea is that there could be some sort of magical influence that makes her think Percy is hot, and she has to figure out how to break free from it while also dealing with her new - found attraction.
Another possible plot twist is that their sparring somehow awakens an ancient prophecy. They initially think it's just a normal sparring session, but then strange signs start to appear. For example, old symbols start to glow on the ground around them as they spar. They then have to figure out what this prophecy means and how their sparring is related to it, all while still dealing with their friendly competition.
A great plot twist could be that they are both being manipulated by a third force. They think they are fighting each other for their own reasons but in reality, they are being used. Maybe a god or a powerful demigod is pulling the strings. This would lead to a moment of realization and then they would have to figure out how to work together to stop the real threat. Also, a plot twist where the Mark of Athena has a different meaning for each of them could be really engaging. It could be that Percy thinks it means one thing and Jason thinks it means another and their interpretations lead to a big misunderstanding before they figure it out.