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.
Maybe they are all transported to an alternate dimension where the rules of their world are different. Percy has to figure out how to use his powers without water, Thalia discovers new aspects of her lightning, and Nico has to deal with different types of underworld creatures. They must find a way to get back home while also helping the people in this new dimension.
Another plot could be set in a modern - day high school where they are trying to keep their demigod identities a secret while also dealing with typical high school problems like bullies and exams. Their different personalities - Percy's laid - back heroism, Thalia's tough - girl exterior, and Nico's brooding nature - create interesting dynamics as they navigate both the mortal and demigod worlds together.
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.
A cool fanfiction idea could be that Percy, Nico, Jason are chosen by Chaos to be its champions in a battle against an ancient evil that is trying to bring total destruction. They are given special powers by Chaos and have to learn to use them quickly.
One plot idea could be them going on a quest together to find a long - lost artifact that has the power to unite the demigod camps. Another could be a story where they discover they have a hidden sibling bond that gives them unique powers when they work together. Maybe a plot where they have to face an ancient enemy that is specifically targeting their family line.
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.
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 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.
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.