The story could develop in many ways. For one, there would be a power struggle. Other powerful beings in the story might feel threatened by Percy's new primordial status. His friends would have to decide whether to support him or try to bring him back to his old self. Percy himself might struggle with his new identity and the responsibilities that come with it. There could also be new enemies emerging, who are interested in either using Percy's power or destroying him.
Well, if Percy becomes a primordial in fanfiction, the story would take an exciting turn. Percy would no longer be just a demigod hero. His new status would attract all kinds of attention. Gods might try to manipulate him or form alliances with him. His old enemies might be too afraid to attack him directly but instead plot against him in more devious ways. Percy would also have to learn to control his new powers, which could be overwhelming. And the places he used to frequent, like Camp Half - Blood, might not be the same for him anymore. He could either be a great protector or a source of chaos, depending on how he adapts to his new form.
If Percy Jackson became a primordial in fanfiction, he would be a force to be reckoned with. Primordials are extremely powerful entities. Percy's transformation could lead to him having the ability to reshape the world according to his will. He could potentially create new realms or change the laws of nature. His personality might also shift, becoming more detached and otherworldly as he adapts to his new primordial state. This would make for a very interesting plot as the other characters try to deal with this new Percy.
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.
The story could develop in many ways. One way is that Percy would start to corrupt the demigod world. He might spread his new - found chaos among the other demigods, turning some of them to his side. Another way is that he could create his own little 'kingdom' of chaos, ruling over a group of misfits. This would put him in direct opposition to the Olympians, who would see him as a threat to their order.
A powerful demigod who has been corrupted by the idea of primordial power could be the main antagonist. They might believe that by allying with a primordial or obtaining their power, they can become greater than the gods. This demigod would then oppose Percy, who stands for the protection of the current order.
They could start off as cautious of each other. Raven might sense the power within Percy that is different from her own, and Percy would be curious about Raven's rather dark and mysterious aura. As they are thrown into situations together, like fighting a powerful demon that is affecting both their worlds, they gradually start to trust each other and develop a bond.
Obviously, the Primordial of Monsters itself could be the main antagonist. It has the power and the motive to cause chaos and destruction, which would put it directly in opposition to Percy and his friends.
It could be a new, powerful Titan that has emerged from the depths of Tartarus. This Titan might be jealous of the eldest primordial's power and wants to either destroy it or take its power for itself. And since Percy is associated with the eldest primordial, he becomes the Titan's target as well.
A possible plot could be that the Primordial Son of Chaos is slowly being awakened by the actions of the modern world. Percy senses this disturbance in the fabric of the cosmos. He then embarks on a journey to find out more about this entity. Along the way, he meets old foes and new friends. The story could involve a race against time as Percy tries to prevent the full awakening of the Primordial Son of Chaos if it's going to bring destruction, or he could be trying to ensure its proper awakening if it's meant to bring balance.
Obviously, the Primordial of Destruction itself would be a major antagonist. It's a powerful and chaotic force that wants to bring about destruction. But also, there could be some demigods who are influenced by the Primordial's power and turn against Percy. They might be jealous of his power or simply be corrupted by the allure of destruction. Another possible antagonist could be an ancient cult that worships the Primordial of Destruction and is trying to bring it back to full power. They would do anything to stop Percy from interfering with their plans.
One possible plot could be that Percy, as a primordial, is seen as a threat by some of the gods. They might try to either control him or get rid of him. Percy then has to fight not only against the traditional enemies like monsters but also against the very gods he once thought were on his side. Meanwhile, he discovers ancient secrets about the primordial beings and his own origin that could change the fate of the entire world of demigods. He might also form new alliances with other primordial - like beings or creatures that are shunned by the normal order of things.