A really interesting plot twist might be that Kakashi, in the process of adopting Naruto, uncovers a conspiracy within the Hidden Leaf Village. There could be some people who oppose Kakashi's decision, not because of Naruto himself, but because they are afraid of what Kakashi might discover about their own misdeeds while getting closer to Naruto.
One possible plot twist could be that Kakashi discovers Naruto has a hidden power that no one else is aware of. This could change the whole dynamic of their relationship. Maybe it's a new type of chakra that only Kakashi can help him control.
Well, a great plot twist could be related to Naruto's past. What if Kakashi finds out some dark secrets about Naruto's family that were hidden from him all this time? It could lead to a whole new arc in the fanfic, with Kakashi having to protect Naruto from those who don't want the secrets revealed.
This adoption could have a huge impact on Naruto's character. He might become more introspective. Since Kakashi is a complex character, Naruto could start to think more deeply about his actions and the world around him. He may also become more reserved as he tries to live up to Kakashi's expectations, but at the same time, he'd still keep his core, energetic self.
One possible plot twist could be that Naruto actually steals something from Kakashi that he thought was unimportant, but it turns out to be a key to a hidden jutsu or a secret mission. Another could be that Kakashi knew Naruto was going to pickpocket him all along and let it happen as part of a training exercise. Maybe Naruto pickpockets Kakashi, but then realizes he has to return the item quickly because it's something that Kakashi needs to save the village.
One possible plot twist could be that they discover their brotherhood in a very unexpected way. For example, during a dangerous mission, Kakashi might get severely injured and in a moment of delirium, he reveals a long - hidden memory that points to their relation. Naruto, being shocked at first, then realizes it explains some of the strange feelings of connection he had towards Kakashi all along.
Maybe Naruto adopts Kakashi in a post - war scenario where Kakashi has lost his purpose. Naruto, seeing Kakashi's lost state, decides to take him under his wing. As a result, Kakashi starts to learn new jutsus from Naruto and they develop a bond that is more like brothers. This would be a great opportunity to explore their characters in a different dynamic.
Well, the plot could revolve around Kakashi providing Naruto with a more stable family - like environment. He might cook for Naruto, help him with his studies at the ninja academy in a more hands - on way, and also be there to support Naruto emotionally when he has nightmares about being alone. This could lead to Naruto growing up more confident and perhaps even developing new skills faster as he has someone constantly guiding him.
One possibility could be a misunderstanding. Maybe Kakashi is framed for something that makes Naruto believe he has betrayed him. For example, an enemy could use a clone of Kakashi to perform a heinous act, and Naruto witnesses it without seeing the full picture.
Well, it could be that in this fanfic, Kakashi discovers a new potential in Naruto. He might train Naruto in some ancient and forgotten ninja arts. This would set Naruto apart from his canon self. Also, their relationship could be explored more deeply, like Kakashi becoming a father - figure to Naruto, and this emotional bond could influence Naruto's growth as a ninja.
A possible plot could be that in a mission gone wrong, Naruto and Kakashi get separated from the rest of the team. They end up in a strange place where they have to rely on each other more than ever. As they face various challenges together, their bond deepens and Naruto realizes his feelings for Kakashi, leading to a kiss.
A really interesting plot twist could be that female Naruto is actually from an alternate dimension where she and Kakashi are already married. In this new world, things are different, and she has to figure out how to make their relationship work in this dimension too. Plus, there could be a character who is jealous of their union and tries to break them apart by spreading false rumors about Kakashi's past, which female Naruto has to deal with.
One possible plot twist could be that their relationship is initially opposed by the village elders. They might see it as unconventional or worry about how it could affect Naruto's role as a potential Hokage. Another twist could be that an old enemy resurfaces and targets Kakashi to get to Naruto, seeing their marriage as a weakness to exploit.