One possible plotline could be Percy having to face some new and terrifying monsters sent by Nyx's enemies. Since Nyx is a powerful figure, there would be many who oppose her, and Percy, as her champion, would be in the line of fire.
Perhaps a plot where Percy has to journey to the darkest corners of the Underworld, which are under Nyx's domain. He might have to retrieve an important artifact for Nyx, facing challenges like treacherous terrains and dangerous spirits along the way. In this fanfiction, it could be that the normal rules of the Percy Jackson universe are bent a bit because of Nyx's influence.
Another plotline could involve Percy exploring the powers he has inherited from Chaos and Nyx. Maybe he discovers unique abilities that no one has ever seen before, like the power to manipulate shadows in a way that's different from a child of Hades. This could lead to him going on a journey to understand the full extent of his powers and how to control them.
Well, Annabeth would definitely be one. She's always been by Percy's side, and in this fanfiction, she might be a bit worried about Percy being the champion of Nyx. She could be trying to help him while also being cautious of Nyx's motives.
One possible plot for a 'Percy Jackson Champion of Nyx fanfic' would be that Nyx chooses Percy as her champion to stop an ancient evil that is rising. Percy would have to train in the ways of Nyx, which are very different from what he's used to. He'd have to learn to harness the power of the night, deal with Nyx's shadowy minions, and find a way to unite the demigods who are skeptical of his alliance with Nyx. As he delves deeper into this role, he uncovers secrets about Nyx's past and how it ties to the future of the demigod world.
One possible plotline could be Percy having to fight against other champions of different deities who see him as a threat. Another is that he has to find a way to combine his new role with his loyalty to his friends and the Olympians. For instance, he may be forced to make a choice between following Pontus' orders that might seem harsh to his friends or standing by his friends and risking the wrath of Pontus.
The Titans could be antagonists. They might see Percy as a threat since he's Nyx's champion. They could try to stop him from fulfilling Nyx's tasks or even try to turn him against Nyx.
Well, perhaps the plot could center around Percy's journey to discover his true self and his purpose. Nyx, being his caregiver, might have her own motives for raising him. Percy could be on a quest to find out if Nyx has some grand plan for him. Along the way, he would encounter various challenges. He might have to battle creatures that are native to Nyx's domain. His powers would evolve in unique ways. For instance, he could have the ability to communicate with nocturnal animals or control the night itself in some small ways. His relationship with Nyx would also be complex, with moments of love and respect, but also times when he questions her actions and decisions.
You can try searching on popular fanfiction websites like Archive of Our Own (AO3) or Fanfiction.net. Just type in 'Percy Champion of Nyx' in the search bar on those sites, and it should show you any available fanfictions related to it.
One common theme is probably Percy's journey as the Champion. It could involve his training, the challenges he faces, and how he overcomes them. Another theme might be his relationship with Nyx, whether it's a master - apprentice kind of relationship or something more complex.
One possible plotline could be Percy having to prove himself to Ares. He might be sent on a dangerous quest to retrieve a powerful weapon that was once Ares'. Along the way, he could face off against other demigods who are jealous of his new position. Another plot could involve Percy trying to balance his loyalty to his friends and his new role as Ares' champion. He may have to make tough decisions that put his relationships at risk.
Well, you could write a fanfiction where Percy Jackson is framed for a crime he didn't commit at Camp Half - Blood. As a champion, he has to prove his innocence while also dealing with the fact that some of his friends start to doubt him. He then embarks on a journey outside the camp, with only a few loyal friends by his side, to find the real culprit and clear his name. This could involve facing various mythological creatures and obstacles along the way.