Perhaps they could time - travel to a point in time where their friendship was just starting to form. They could see how their early interactions unknowingly set the course for all their future adventures. Or, they could be sent to a time when a great villain from their present was a young and innocent person, and they have to decide whether to try and change the villain's future or let things play out as they originally did.
One idea could be that Kim and Ron get stuck in a time loop within a particular historical event. They have to keep reliving the same day until they figure out how to correct an anachronism that's disrupting the time - space continuum. Another could be that they travel to the future and see versions of themselves that have changed in unexpected ways due to different life choices.
Maybe in the fanfiction, Kim and Ron find a hidden power within the time - traveling device during 'Sitch in Time'. This power allows them to visit different key moments in their past adventures but also attracts the attention of a new villain who wants to steal this power for their own evil plans. So they have to protect this power while still trying to fix any disruptions in time.
Monkey Fist is often a popular choice. His villainous nature and his connection to martial arts and ancient artifacts can add a lot of intrigue to a time - travel based fanfiction. He could be chasing Kim and Ron through different time periods, trying to steal some powerful relic.
Perhaps in this fanfiction, Kim might lose some of her powers during the time - traveling adventures in 'a sitch in time 2'. She then has to rely on her wits and the help of her friends like Ron and Rufus in a more creative way. For example, she might use her knowledge of history to outsmart the bad guys instead of just relying on her usual martial arts and gadgets.
Their relationship could develop more quickly in the fanfiction. For instance, during the 'Sitch in Time' events, they might have a moment of realization where they understand their feelings for each other more deeply due to the high - stakes time - traveling situation. They could start to act more like a couple earlier than in the original story.
Perhaps in the fanfiction, they decide to have a destination wedding. But on the way to the location, they get caught up in a mystery that they can't resist solving. So, instead of focusing on the wedding, they are off on an adventure. This adventure could strengthen their bond even more and make their wedding, when it finally happens, even more special.
There could be a time - guardian character. This character could be an ancient being that has been protecting the timelines and appears to help Kim understand the true nature of time - traveling and the rules she must follow to set things right.
In this 'Kim Possible Kidnapped Fanfiction', there could be a scenario where Kim is kidnapped while on a mission in a foreign country. The kidnappers could be local criminals who mistake her for someone else. Or maybe a mad scientist kidnaps her to use her as a test subject for his dangerous experiments. Another plot could involve a group of ninjas kidnapping Kim as part of a long - standing feud with her family's martial arts legacy.
One idea could be an OC who is a new villain in Middleton. This OC could have a unique power like the ability to manipulate technology remotely. They start causing chaos by hacking into all the city's systems. Another idea is an OC that is a long - lost relative of Kim and comes to live with her family. This OC has a different set of skills and gets involved in Kim's missions in unexpected ways. Or perhaps an OC who is an alien exchange student at Kim's school and has to hide their true identity while also helping Kim fight off intergalactic threats.
One possible plot idea could be that they face unexpected challenges while preparing for the baby. Maybe they have to deal with villains who try to take advantage of Kim's pregnancy-induced vulnerability. Another could be that they struggle to balance their crime - fighting lives with the new responsibilities of parenthood.
Another plot could be that Ron and Harry find a hidden, ancient magic in the Forbidden Forest. This magic gives them the ability to communicate with magical creatures in a much deeper way. They use this new - found ability to unite the different factions of magical creatures against a common enemy, like a dark wizard who wants to use the creatures for his own evil purposes.