There could be new entities created by Chaos itself that turn against them. Maybe some primordial beings that were once dormant but are awakened by the arrival of Percy, Nico and Thalia. These beings might be jealous of the attention Chaos gives to them or simply see them as invaders in their chaotic domain.
The Titans could still be their enemies. Even in the realm of Chaos, the Titans might see them as a threat to their potential return to power. Kronos, if he somehow still has a presence, would likely oppose them. He would not want these three, especially Percy who has defeated him before, to gain more power from Chaos.
In the fanfiction, they could be given important missions. Maybe they are tasked with restoring balance in a part of the Chaos realm that has been thrown into disorder. Percy's leadership skills, Thalia's combat experience, and Nico's knowledge of the underworld could all be put to good use. They would have to work together, which might not be easy at first given their different personalities. But as they face challenges, they would grow closer and become a more effective team.
They could be sent on epic quests by Chaos. Maybe they have to retrieve some powerful artifacts that were lost in the chaos of creation. Along the way, they would face numerous challenges and meet all kinds of strange creatures. Percy would use his strategic thinking, Nico his knowledge of the underworld, and Thalia her leadership skills to overcome obstacles and make their way towards their goal.
The story would develop with them exploring the Chaos realm. They might discover ancient secrets and long - lost powers. Their relationships with each other would evolve. For example, Thalia and Nico might bond over their shared experiences in the face of the new and terrifying things in the Chaos realm. Percy could act as the mediator between them at times. They would also have to deal with the politics and power struggles within the Chaos realm. There could be factions that want to use them for their own ends, and they would have to navigate through these tricky situations while still trying to achieve their own goals.
One possible plot could be that Percy and Thalia are tired of the constant battles and politics in their current world. Chaos offers them a new beginning. They join Chaos' forces and are trained in unique ways. Percy might use his water - controlling abilities in new and unexpected ways under Chaos' guidance. Thalia could also enhance her skills with lightning. Together, they go on missions to restore balance in different realms that are in chaos (in a non - traditional sense).
It could be the agents of Order who see Percy and Thalia joining Chaos as a threat to the balance they strive to maintain. They might send their best warriors to stop Percy and Thalia from carrying out Chaos' plans.
I really liked a fanfic where Nico discovers a hidden power related to Chaos and Percy and Thalia have to help him control it. The story delved deep into Nico's insecurities and how his friends supported him. It was really heartwarming and full of suspense at the same time.
In this fanfiction, it could be that Percy, Nico and Jason are chosen by Chaos for a special mission. Chaos might have seen something unique in them, like Percy's leadership skills, Nico's connection to the underworld and Jason's strategic mind. They join Chaos and are part of a team that has to go on a quest to find some lost artifacts that are crucial in maintaining the balance between order and chaos in the universe. Along the way, they face many challenges, make new friends and enemies, and grow as characters.
Their relationships could develop in many ways. At first, Percy and Thalia might have some friendly bickering as they used to, but with Nico there, they start to form a more united front. Nico, being a bit more withdrawn, might gradually open up to them more as they face challenges together. Percy could use his natural leadership skills to bring them together, and Thalia's fierce loyalty would make her a great ally for both of them. As they rely on each other more in the chaotic situations, their bonds would strengthen into deep friendships.
One popular trope is the 'Chosen by Chaos' trope. For example, in many fanfictions, Percy, Nico or Thalia are chosen by Chaos for a special task. It gives them extraordinary powers and sets them on a grand adventure. Another is the 'Power - up' trope where they gain new abilities from Chaos.
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.