It could be a young woman who is a stowaway on a ship and gets discovered and kidnapped by pirates.
The main character might be an orphan who has been living on the streets. One day, they are lured onto a pirate ship under false pretenses and are kidnapped. This character could have hidden skills or a strong will that helps them deal with the pirate crew.
It could be a young adventurer. This type of character would be full of curiosity and a sense of exploration. Their kidnapping by pirates would be a major setback to their adventure plans, but they would also be quick to look for ways to turn the situation around.
It could be a young child who strays too close to the sewers where Pennywise lurks.
A young adventurer could be a great main character. They are always exploring new places, so it's likely they could end up in the wrong place at the wrong time and get kidnapped by witches.
Well, it could be about a person, maybe a young adventurer, who is captured by pirates. The story might then revolve around their attempts to escape or adapt to life on the pirate ship.
It could be a new character created specifically for the fanfiction. Maybe a young scientist who is working on a project related to the super - soldier serum. Since Bucky has a history with the serum, this would create an interesting dynamic.
Perhaps it could be a minor character from Twilight who somehow ends up in a situation where they are kidnapped by a creeper. This would give the writer a chance to explore that character more deeply and in a completely different context. For example, a character like Jessica from Twilight could be the main character. She's not a central figure in the original story, but in this fanfiction, she could have a whole new adventure.
It could be Robin, the Boy Wonder. If Catwoman kidnapped Robin, Batman would surely be on a mission to rescue him. Robin is young and inexperienced compared to Batman, so he could be an easy target for Catwoman, and his rescue would make for an exciting story.
It could be an over - enthusiastic fan who has always wanted to meet the Jokers. They get kidnapped by accident during one of the Jokers' wild stunts, and then they have to deal with the crazy situation.
Well, it's possible that a powerful and evil pirate lord could be the main antagonist in 'hermione is a pirate fanfiction'. This pirate lord might control a large part of the seas and sees Hermione as a threat to his dominance. He could have a large fleet and many ruthless henchmen. He might try to capture Hermione to either make her join his crew or to simply get rid of her because she is disrupting the order he has established in the pirate world.
It could be the navy. They see pirates as outlaws and would be determined to capture Percy and his crew. They might have better - equipped ships and more trained soldiers, making them a formidable foe for Percy and his fellow pirates.