What could be the plot of a fanfiction where Nico kidnaps Percy?

One possibility is that Artemis has been misinformed. Some enemy of Percy has tricked her into thinking that Percy is a danger to the demigods. So she kidnaps him to stop him from causing harm. But as she keeps Percy captive, she slowly realizes that she has been deceived when Percy starts to explain his side of the story and the real threats he has been fighting against.

Well, perhaps Aphrodite kidnaps Percy because she wants to play matchmaker. She might see some potential love connection for him that he's been avoiding, so she takes matters into her own hands. Maybe she has a grand plan to set him up with a certain demigod or even a mortal, and she believes that by kidnapping him, she can force him to face his romantic destiny.

Perhaps in the fanfiction, Apollo kidnaps Percy because he thinks Percy has a connection to a prophecy that could either save or destroy the world of the gods. Apollo, being a god of prophecy himself, wants to control the outcome. So, he takes Percy away from his friends and allies to figure out how to use this connection to his advantage.

In a 'Percy and Nico are betrayed' fanfiction, perhaps they are betrayed by the gods. The gods, fearing their growing power, might spread lies about them among the demigods. Percy and Nico then have to fight not only against the false accusations but also the demigods who turn on them. They would have to find a way to clear their names and prove their loyalty.

Well, it could be that Percy yells at Nico because he feels Nico is being too reckless in a dangerous mission. Maybe Nico is about to do something that could endanger the whole group, and Percy, being the protective type, loses his temper.

In this fanfiction, perhaps Percy adopts Nico after Nico has been ostracized by the other demigods. Percy realizes that Nico needs a safe space. So he offers his home. As time passes, they start to understand each other better. Nico might open up about his past traumas to Percy, and Percy would use his own experiences to help Nico heal and feel like he belongs.

Annabeth would be furious. She'd immediately start planning a rescue mission. She might call on all of Percy's friends and allies at Camp Half - Blood. Annabeth would use her strategic mind to figure out where Nico has taken Percy and how to get him back.

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.

Well, perhaps Percy and Nico could be transferred to Hogwarts through some sort of magical accident. Maybe they'd have to deal with the different magical system there compared to their own world. They could make new friends among the Hogwarts students and get involved in the typical Hogwarts adventures like the Triwizard Tournament or dealing with a new dark threat.

Perhaps in the fanfiction, Nico has been tricked by an enemy. This enemy convinces Nico that Percy is a threat to their world. So, Nico decides to take matters into his own hands. Another possibility is that Nico's own internal demons, related to his past traumas and his complex relationship with the gods, drive him to see Percy as an obstacle that needs to be removed.