It could be a young child who strays too close to the sewers where Pennywise lurks.
Perhaps an adult who is investigating the strange disappearances in Derry. They get too close to the truth and are then kidnapped by Pennywise. This character would likely be strong - willed and determined to survive and expose Pennywise.
The plot might involve a character being lured into Pennywise's lair, perhaps by the allure of missing things or people. Pennywise could use his shape - shifting abilities to deceive the kidnapped character throughout their captivity.
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 woman who is a stowaway on a ship and gets discovered and kidnapped by pirates.
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.
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.
A detective - style character could be the main character. This could be a human or an animal detective who is hired to find the kidnapped lemon. They might have a special connection to fruits, like they grew up on an orchard, and they feel a sense of duty to rescue the lemon. They would then go on a journey, following clues and interrogating suspects.
The kidnapped victim could be the main character. They would be the focus as they struggle against Jeff. For example, it could be a young girl who shows great courage throughout the ordeal.