In this fanfiction, it could be that they are sent back in time by an ancient power. When they arrive in the past, they are met with a version of themselves that are much more naive. The kiss might happen as a form of comfort between them, especially when they see the challenges that lie ahead in this different time. This event could set off a chain of events where they have to balance their relationship, their mission to return to their own time, and their desire to fix the past.
Maybe the time travel is caused by a mysterious time - space ninjutsu. In the past, Naruto and Sasuke find themselves in a world where their actions can have a huge impact on the future. The kiss could be a spontaneous reaction to the realization that they are the only ones who truly understand each other across time. As the story progresses, they might try to prevent certain tragedies from happening in the past, all while dealing with their new - found and complicated relationship.
In this type of fanfiction, the time travel might be a result of a forbidden scroll or an experiment by a rogue ninja. When Naruto and Sasuke go back in time, their relationship is different from what it was in their original time. The kiss could be a turning point where they start to understand their feelings for each other on a deeper level, perhaps realizing that their bond is stronger than just friendship or rivalry.
One possible plot twist could be that Sasuke, upon traveling to the past, accidentally changes a small event that has huge ramifications in the future. For example, he might prevent a key encounter that led to a character's development, and as a result, the entire power balance in the ninja world is altered. Another twist could be that Sasuke's presence in the past is somehow detected by an ancient and powerful force, which then tries to either use him or destroy him. Or perhaps, Sasuke discovers that his own past self is not as he remembered, and there are hidden motives or secrets that he was unaware of before.
Maybe they travel back to their early days at the ninja academy. Naruto, who now has all his future knowledge, tries to befriend Sasuke in a different way. But Sasuke, being suspicious, thinks Naruto has some ulterior motive. This leads to a whole new set of comical and at the same time tense interactions between them as they both have to deal with their past selves and the changes they want to make.
In such a fanfiction, they might try to prevent some of the tragedies that occurred in their own time. For example, Naruto could stop the Uchiha massacre, saving Sasuke's family and potentially changing Sasuke's entire path. Sasuke, on the other hand, might use his knowledge to help the ninja world avoid future wars. They could also meet their younger selves and impart wisdom or skills that they learned in their original timeline.
One great Sasuke, Naruto, and Sakura time travel fanfiction is 'Time - Twisted Bonds'. In this story, they are sent back to their childhood days with their present - day knowledge. It's really interesting to see how they interact with their younger selves and try to change things for the better. Another good one is 'Journey Through Time' where they travel to different points in the Naruto timeline and face challenges that were not part of the original story.
A popular one is 'Sasuke's Time - Twisted Journey'. In this fanfic, Sasuke goes back in time and has to deal with his past self. It's full of action and emotional moments. The author does a great job of exploring Sasuke's character in a new light, as he grapples with his past mistakes and tries to make amends.
Well, while I haven't come across such a fanfiction myself, it's not out of the realm of possibility. Fanfiction often takes existing characters and relationships and twists them in unexpected ways. Given the popularity of Naruto, Sasuke, and Sakura, some fans might be interested in exploring this rather unconventional scenario in their creative writing. However, it might also be a subject that some fans would find too far - fetched or against the spirit of the original story.
In this fanfiction, it might be that Sasuke got injured during the mission. Naruto, in a moment of relief after saving Sasuke's life, kissed him. This act could be the start of a new dynamic in their relationship, where they have to confront their feelings for each other while still completing the mission at hand.
Another plot could be that they travel to a time when the Akatsuki was first formed. Naruto might try to persuade the members to choose a different path. Sasuke could explore the reasons behind the Akatsuki's creation more deeply. Sakura could use her skills to heal some of the wounds that led to the formation of the Akatsuki in the first place.
A great plot twist could be that they time travel into the bodies of their younger selves but with their current godlike powers. They then have to deal with the reactions of their friends and family who don't understand what has happened to them, while also trying to use their new - found situation to prevent some future disasters.