A plot could involve the kidnapped character being from a different time or dimension. The pirates are initially confused by their strange behavior and gadgets (if any). As the character tries to find a way back home, they introduce the pirates to new concepts and technologies, which changes the pirates' view of the world and their way of pirating.
Maybe the kidnapped person is actually a long - lost heir to a powerful kingdom, and the pirates plan to ransom them back to that kingdom. As the story progresses, the kidnapped character forms an unexpected bond with one of the pirates and they start to plot their escape together while also dealing with the politics of the ransom situation.
A great plot for Beast Pirates OC fanfiction could be an OC who is a doctor with a mysterious past. The OC joins the Beast Pirates under false pretenses, claiming to be able to create a super - soldier serum using Devil Fruit powers. As they work within the group, they secretly try to find a way to cure the madness that seems to be a part of the Beast Pirates' nature. Along the way, the OC has to deal with the various power - hungry and unpredictable members of the pirates, like Jack and Queen, while also hiding their true intentions.
One idea could be that Jake and his crew discover a new part of Neverland filled with magical creatures that can talk and have their own unique abilities. Another could be a time - traveling adventure where they go back to the days when Captain Hook was a young pirate just starting out. Or perhaps they find a mysterious treasure map that leads them to a place where the rules of Neverland don't apply.
One idea could be a crossover where Naruto's ninja skills are combined with the Kuja Pirates' unique abilities. For example, Naruto could teach some of the pirates his shadow clone jutsu, and in return, the pirates could show him how to use their weaponry more effectively.
One plot idea could be that Todoroki is kidnapped by a villain who wants to use his powerful quirk for their own evil plans. His friends then embark on a dangerous rescue mission. Another could be that it was a case of mistaken identity and Todoroki has to figure out how to escape while also dealing with the kidnappers' demands. Or perhaps Todoroki is kidnapped by a group who wants to study his unique genetic makeup related to his quirk.
Another plot could be that Rapunzel is kidnapped by a mysterious figure from her past that she doesn't remember. As she's held captive, she starts to have flashbacks of her early childhood and discovers secrets about her family. Meanwhile, Flynn Rider and the others are on a frantic search for her, and Rapunzel has to find a way to signal them while also dealing with the revelations about her past.
Well, perhaps Katara is kidnapped by a bounty hunter who has been hired by someone who has a vendetta against the Avatar's team. The kidnapper could be taking her to a far - off and desolate location. Then, Aang and the others have to track her down through various difficult terrains. Or, it could be that she's kidnapped by a group of dark benders who want to study her waterbending to find a way to corrupt it. They might keep her in an underground lair filled with all sorts of dark magic - like contraptions.
One idea could be the protagonist discovers a hidden power within themselves while being held captive by the demons. This power could be the key to their escape or a way to turn the demons' own plans against them.
One plot idea could be that Sasuke kidnaps someone he believes has information about a hidden enemy. He then has to deal with the moral implications as he realizes the person is innocent. Another could be a love - driven kidnapping, where Sasuke kidnaps someone he secretly loves but is too conflicted to show it in a normal way. And perhaps a third idea is that Sasuke is forced to kidnap someone under a mind - control spell and has to fight against the control to free the victim.
One idea could be that the kidnapper has a mistaken identity and thought the miko was someone else with great power. Another could be that it's part of a larger scheme to disrupt the miko's religious order. Or perhaps the kidnapper has a personal vendetta against the miko's family and is using her as leverage.
One idea could be that Izuku is kidnapped by a group who wants to use his knowledge of hero strategies against the heroes. They hold him hostage in an abandoned building. Another could be that a villain with a grudge against All Might kidnaps Izuku as a way to lure All Might into a trap. Maybe a group of anti - quirk fanatics take Izuku because they believe his powerful quirk is a threat to their cause.