A new, evil racing car that has just entered the circuit and sees Lightning McQueen as the biggest threat to his own success. This new car is desperate to win and thinks that by kidnapping Lightning, he can eliminate the competition.
It could be Chick Hicks. He's always been jealous of Lightning McQueen and might resort to kidnapping to get him out of the way for future races.
One possible plot could be that a rival racing team kidnaps Lightning McQueen to prevent him from competing in a crucial race. They hold him in a secret location, but his friends Mater and Sally start a search. Mater uses his unique knowledge of the backroads to track down leads, while Sally uses her charm and wits to question other racers. In the end, they manage to find Lightning just in time for the race.
In this fanfiction scenario, if Lightning McQueen were kidnapped, perhaps Mater would be the first to notice his absence. Mater could then start a search, rallying all the cars in Radiator Springs. They might look everywhere from the deserts to the highways, following any small clues they can find, like a strange tire mark or a bit of Lightning's paint that was left behind.
Another reason could be related to his pride. Chick Hicks has always been in McQueen's shadow. He might believe that by kidnapping McQueen, he can prove that he is the more dominant one. He wants to show that he can control McQueen's fate, which in his twisted mind, would make him feel superior in the racing community. He could also be trying to break McQueen's spirit so that he will no longer be a threat to him in future races.
It could be an old enemy of Keith's, someone from his past who has a vendetta against him. Maybe a former rival from his days in the military academy who has now turned to more devious means.
In some creative fanfiction, it could be an alternate version of Spiderman himself from a different dimension. This Spiderman has gone bad and kidnaps a fan from our dimension as part of some grand, dark plan that involves crossing dimensions and causing chaos.
A power - hungry nobleman from a neighboring land could be the kidnapper. He might believe that by having Rapunzel in his possession, he can gain some sort of political advantage or use her as a bargaining chip against her kingdom.
It could be Orochimaru. He's always been interested in obtaining powerful individuals for his experiments, and Naruko with her unique abilities would be a prime target.
It could be a new villain that has emerged, someone who is jealous of Gohan's power and wants to make it his own. This villain might be from a far - off planet and has heard of the Saiyan legend.
It could be a group of rogue Decepticons who are acting on their own. They might not follow Megatron's orders but still see value in kidnapping Arcee. Maybe they have a personal vendetta against her or think they can get rich by selling her to the highest bidder in the Cybertronian underworld.
Maybe it's a group of villains working together. They could be from different factions but united by the idea that Izuku has the potential to become a huge threat to their plans. They might kidnap him to either eliminate him or turn him to their side. Also, it could be a lone, obsessed fan of a villain who wants to prove themselves by bringing Izuku to their idol.