Another idea is that the lemon was kidnapped by a group of fruit enthusiasts who believe this lemon is the key to creating the perfect lemonade recipe. They've been searching for the right lemon for years, and when they find this one, they resort to kidnapping to keep it away from their competitors. So the story could be about the lemon's escape attempts and how it outsmarts these over - eager fruit lovers.
One idea could be that the kidnapped lemon is actually a special, magical lemon. Maybe it has the power to grant wishes when it's juiced, and the kidnapper wants to use it for their own greedy desires. For example, they could be planning to sell the lemon's juice to the highest bidder in a world where magic elixirs are highly sought after.
One idea could be a story where the kidnapped kids form a strong bond among themselves in captivity and work together to outwit their captors. For example, they might use their unique skills like one being good at puzzles to unlock doors or another having a great sense of direction to find an escape route.
One idea could be that a new vampire clan kidnaps Bella to use her as bait to lure Edward into a trap. They might want to challenge the Cullen family's power in the vampire world.
One plot idea could be that Mowgli is kidnapped by a group of poachers who mistake him for a rare forest spirit. They plan to sell him to a wealthy collector. Another could be that a rival wolf pack kidnaps Mowgli in an attempt to use him as a bargaining chip against his own pack. Maybe a group of outcast monkeys kidnap Mowgli to force him to teach them the ways of the man - village so they can gain power over the jungle.
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.
One idea could be that a rare and powerful Pokemon is kidnapped by a mysterious organization aiming to use its power for evil. A young trainer then sets out on a dangerous journey to rescue it. Another could be a Pokemon being kidnapped from a Pokemon sanctuary, and the local Pokemon community unites to get it back.
Maybe Mirajane is kidnapped by a dark wizard who has a vendetta against her family. In the fanfiction, the wizard could be trying to force Mirajane to reveal the secrets of her family's magic. Her Fairy Tail comrades would have to figure out where she is and how to defeat this powerful foe.
Well, a plot could involve Spock kidnapping someone to protect them from a greater danger that he knows about but others don't. For instance, he kidnaps a young, talented cadet who has a special power that an enemy race wants to exploit. He takes the cadet to a hidden location on a Vulcan outpost to keep them safe until he can figure out how to deal with the approaching threat. Or perhaps he kidnaps a diplomat who is unknowingly carrying a virus that could wipe out Vulcan, and he needs to keep the diplomat isolated until a cure can be found.
Maybe the witches kidnapped the character because they believe the character is the key to a prophecy. The character could then try to find out more about this prophecy and use it to their advantage, like befriending some of the nicer witches to help them escape. This could involve a lot of exploration within the witches' lair, finding hidden passages and ancient scrolls that hold the secrets of the prophecy.
One idea could be that Serena is kidnapped by a mysterious group who wants to use her unique abilities (if she has any in the fanfic's universe) for their own gain. For example, if she's a great athlete, they might want to force her to compete for them illegally. Another plot could involve a jealous rival who kidnaps Serena to stop her from achieving a great success, like winning a big tournament. Or perhaps Serena is kidnapped by someone who mistakes her for someone else and the whole story is about her trying to convince them of their mistake while also trying to escape.
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.