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.
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).
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.
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.
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.
Yes, there are quite a few. You can start by looking on fanfiction.net or Archive of Our Own. There, you'll find various takes on their relationship. Some might focus on how their initial meeting could have led to a different kind of bond, while others could explore a scenario where they have to work together in a chaotic situation and feelings start to develop in the midst of it.
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.
The main characters are Percy and Thalia, of course. Percy, with his water - based powers and heroic nature, often takes the lead in many situations. Thalia, as a strong and fearless demigod, is right there with him. They both interact with the concept of Chaos in different ways in these fanfictions.
Obviously, Percy and Thalia are the main ones. Percy, the son of Poseidon, is often brave and impulsive. Thalia, daughter of Zeus, is strong - willed. Their love for chaos makes them different from other demigods. They are the focus as they navigate through the world of chaos and their feelings for each other in this fanfiction.