One possible scenario could be Percy being betrayed by a primordial who he thought was an ally. Maybe the primordial promised him power to defeat a common enemy but then turned on him at a crucial moment, leaving Percy vulnerable and alone against a greater threat.
In some fanfictions, Percy might be betrayed by a primordial because of a misunderstanding. For example, he could be misinterpreted as a threat to the primordial's domain or plans. The primordial, without fully understanding Percy's intentions, might take actions that seem like a betrayal to Percy. This could lead to a complex story of Percy trying to clear his name and regain the primordial's trust, or having to fight against the primordial who is now his enemy.
In Camp fanfiction, Percy could be betrayed when the camp leaders are deceived by false evidence against him. Let's say an enemy creates some fake proof that Percy has been colluding with their side. The leaders, without fully investigating, might turn on Percy. Also, there could be a love - related betrayal. If Percy has a romantic interest in the camp, the person he likes could be forced by their family or some external pressure to break Percy's trust and use his feelings against him, for example, to make him give up his position in the camp or some important secrets.
Perhaps Percy would try to understand the primordial's reasons for the betrayal. He's a smart and empathetic character. He might think that there was some misunderstanding or that the primordial was forced into it. So, instead of immediately retaliating, he could try to communicate with the primordial to clear things up. If that doesn't work, then he would be more likely to take a defensive stance rather than an offensive one, at least until he fully understands the situation.
Well, it could start with Percy being framed for a crime he didn't commit by the gods. This false accusation makes him feel extremely betrayed. He then has to go on the run while trying to prove his innocence. Along the way, he meets other outcasts and together they form a resistance against the gods. They might try to find a way to hold the gods accountable for their actions and create a new order where demigods are treated more fairly.
One possible scenario could be that in the fanfiction, some evil organization captures Percy and tries to figure out his powers related to being a demigod. They might subject him to various tests like trying to measure the limits of his ability to control water, or how he can heal from injuries that would be fatal to normal humans. Another could be that they experiment on his connection to the Greek gods, perhaps trying to sever or manipulate it in some way.
Perhaps in a scenario where Percy is about to sacrifice himself for the greater good. Triton, seeing Percy's selfless act, is so moved that he cries. Another situation could be when Percy is being wrongly accused and is facing great danger, and Triton, who knows Percy's true nature, cries out of frustration and worry for him.
Percy might struggle with his new identity. He has been a demigod for so long, and suddenly becoming a primordial god means he has to re - evaluate his place in the world. He may miss his old life, his friends, and the simplicity of being a demigod. Adjusting to the new powers and responsibilities is not going to be easy.
In a 'Percy Jackson Dies' fanfic, one possible scenario could be that he sacrifices himself to save his friends during an epic battle against a powerful new enemy. Maybe a horde of monsters that are immune to his usual powers overwhelm him while he's trying to buy time for his friends to escape.
One possible plot development could be Percy feeling extremely hurt and isolated after the betrayal. He might go off on his own to find a way to prove his worth again. Maybe he'll encounter some old enemies who now see him as vulnerable and try to take advantage of his situation.
One possible scenario could be that Percy sacrifices himself to defeat a powerful enemy. Maybe he uses his powers to hold off a huge monster that is about to destroy Olympus and in the process, he gets fatally injured and dies. Another could be that he is betrayed by someone he trusts, which leads to his death. For example, a demigod who is jealous of Percy's popularity and powers might make a deal with the enemy and set Percy up.
One scenario could be that Percy has some sort of magic spell cast on him that makes him smaller. Maybe a mischievous god or a powerful enemy uses a spell to shrink him for their own amusement or to gain an advantage in a battle. This would lead to some interesting situations where Annabeth has to protect him in a different way than usual.