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.
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 Nico, being a bit more withdrawn, might gradually open up to them more as they face challenges together.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.
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.
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.
Well, they could be in a situation where Chaos has plans for them that conflict with their own loyalties. Percy might be hesitant because he has friends and a life back at Camp Half - Blood, Thalia has her Hunters, and Nico has his own reasons to be cautious. But Chaos shows them visions of a future where if they don't cooperate, everything they know will be destroyed. So they embark on a journey together. Along the way, they face challenges like traversing through shifting landscapes in the Chaos realm. They also have to deal with their own internal conflicts as their personalities clash at times while trying to work towards the goal set by Chaos.
One challenge is the jealousy of other gods. Since they are new gods, the older, more established gods might not like the attention they get or the new ideas they bring. Another challenge is controlling their powers. As mentioned before, going from demigod to god means a huge jump in power level, and it's not easy to get used to. For example, Percy might accidentally flood a city while trying to create a small puddle for fun.