It could be Klein. He is Kirito's friend and has his own set of skills. He might gather a group of other players who are also concerned about Kirito's disappearance and together they try to rescue him from Kayaba.
Another plot could be that Kayaba has some sort of vendetta against Kirito. Maybe he sees Kirito as a threat to his own power and control within the virtual world. So, by kidnapping him, he aims to either break Kirito's spirit or get him out of the way so that he can maintain his dominance.
One interesting Naruto Kayaba fanfiction could be about Kayaba somehow being transported to the Naruto world. Maybe he uses his knowledge of technology to create new jutsu or devices. For example, he could combine his virtual reality skills with ninjutsu to create training simulations that are far more advanced than what the ninja in Naruto are used to.
Yes, there might be. In the world of fanfiction, all sorts of creative and often out - of - the - ordinary scenarios are explored. Given Kirito's popularity in the Sword Art Online universe, it's not unlikely that some fans have written stories where he is involved in a kidnapping situation, either as the victim or perhaps in a more complex plot twist where he is wrongly accused of kidnapping. However, the quality and nature of such fanfictions can vary greatly.
No, it's not common at all. Thor is usually depicted as a heroic and noble character in fanfiction. Kidnapping goes against his basic nature of protecting the weak and upholding justice.
First, do your research on both Naruto and Kayaba. Know their personalities, abilities, and the worlds they come from. For Naruto, study the different ninja techniques, the village structure, and the relationships between characters. For Kayaba, understand his role in his original story, like his skills in creating virtual worlds. Then, come up with a unique plot idea. It could be a crossover concept, or something that changes the existing Naruto story in an interesting way.
One common theme is the heroic rescue. In these fanfictions, Max and 99 often use their unique spy skills to outwit the kidnappers and save the day. Another theme could be the emotional turmoil of the kidnapped character, exploring their fears and hopes while in captivity.
In some fanfictions, they could start as rivals. Maybe they both enter a tournament in the virtual realm. At first, they are competing against each other, but as they get to know each other better during the tournament, they start to develop feelings and eventually become allies and more.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions from various fandoms, including Get Smart. There may also be some on FanFiction.net.
You can try some popular fanfiction websites like Archive of Our Own. There are a lot of different stories there and you can search specifically for kirito x female kirito fanfiction using the search function.