A cool plot could be that they are both invited to a special demigod tournament. They start off as rivals but then realize that they need to work together to defeat the real threat, which is a group of rogue demigods who want to take over the camp. As they fight side by side, their brotherly bond strengthens.
Maybe they discover they have a long - lost relative who is in danger. So they team up, Percy using his water powers and Nico his underworld powers to fight the dark forces that are after their relative. During this, they grow closer as brothers and understand each other better.
Maybe they could have a story where they discover a secret about their family's past together. They'd have to deal with the revelations and how it affects their relationship. For example, they might find out that there was a powerful ancestor and they have to figure out how to use or protect the knowledge of this ancestor. This would involve a lot of character growth for both of them as they learn more about themselves through their family history.
Perhaps they go on a quest to find their long - lost family heritage. Along the way, they face various challenges that test their brotherly bond. They might have to cross a dangerous river that only Percy can navigate, but Jason has to use his wind powers to keep them from being swept away, while Nico uses his underworld powers to fend off the ghosts that lurk in the water.
One possible plot could be that they discover they are brothers through a series of magical events. For example, a powerful oracle reveals the truth. Then they have to deal with the shock of this new relationship while also facing their common enemies. They might train together to combine their unique powers and protect their world from threats.
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.
There could be a story where Percy is submissive in a battle - training scenario. Nico, who has unique battle strategies, is in charge of training Percy. Percy has to follow Nico's every order, which at first he resents but then realizes the value. In a different plot, they could be in a time - travel adventure, and Percy is submissive as Nico is the only one who can navigate the time - streams. They go back to important events in their pasts and Percy has to do as Nico says to not disrupt the timeline. Also, a plot where they are in a sort of magical contract situation, and Percy is submissive to Nico until certain conditions are met, during which time they face internal and external struggles and grow closer as a result.
One idea could be a school competition where Percy and Nico have to team up against other demigods. They could use their unique powers in unexpected ways to win, like Percy using his water control to create cool water sculptures as part of an art contest, and Nico summoning shadowy creatures for a drama performance.
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.
One idea could be that Percy and Triton have to team up to save the underwater kingdom from a new and powerful threat. They start off distrusting each other because of their different upbringings, but as they face challenges together, they learn to rely on one another.
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.
Perhaps a plot where Nico discovers a hidden secret about Percy's past that has the potential to change their relationship. This could involve some sort of prophecy or long - lost family connection that they have to navigate together.