In this fanfiction, perhaps Serena is captured by an evil organization. They might be after her special powers or knowledge. Then, her friends would start a rescue mission.
In the 'Serena gets captured' fanfiction, it's possible that Serena is lured into a trap and captured. Once captured, she might be forced to endure difficult situations. For example, she could be interrogated about secrets she holds. Her friends would then have to figure out where she is being held and how to free her. This could involve them facing off against powerful guards or solving complex puzzles to reach her.
In a 'naruto gets captured' fanfiction, he might be tortured for information. His captors could be after the secrets of his Nine - Tails chakra. They may try to use him as a bargaining chip against Konoha.
Well, in this fanfiction, perhaps Steven could be held captive by an old enemy. Maybe he'll have to use his wits to escape, like finding a weakness in the prison's security system.
Well, perhaps Gengar is captured by a powerful trainer. The trainer might use a special Poké Ball to catch it. Then, Gengar could try to escape from the ball by using its ghostly powers.
In this fanfiction, Luffy might be used as a bargaining chip by his captors. Maybe they'll try to exchange him for something valuable, like a powerful Devil Fruit or a large amount of treasure. His crew would then surely launch a rescue mission, facing many challenges along the way.
Well, in such a fanfiction, Sora might be held in a dark and gloomy dungeon. Maybe some old enemies from the original story could be behind the capture, seeking revenge.
Well, he could be held by a villain group who wants to find out the secrets of his power. Maybe they'll try to study his One For All quirk.
It could be a rival group. They might be jealous of Serena's abilities or resources and capture her to gain an advantage.
Well, if Naruto is captured by Orochimaru in fanfiction, one possibility is that Orochimaru wants to use Naruto as a bargaining chip against Konoha. He may think that by having Naruto in his grasp, he can force the Hidden Leaf to meet his demands, like giving him access to certain forbidden jutsu or secret scrolls. Another aspect could be Orochimaru's curiosity about Naruto's ability to master new jutsu so quickly. He might want to study Naruto's mind and body to find out the secret behind his growth as a ninja.
He might be interrogated by the captors. They could try to extract information about the Sith, the Empire's secrets, or his own powers. Maybe they would attempt to turn him against the Emperor, using various means like appealing to his remaining humanity or threatening him with things he values.
In this fanfic, Naruto might be tortured for information about the Hidden Leaf. The Akatsuki are known for their ruthless ways, so they could use various jutsu to make him talk.