Well, a major plot twist could be that when they go back in time, they find out that their past selves already knew they were coming. Maybe in the future, they somehow managed to send a message back. This would completely change the dynamic of how they interact with the past. Also, they could discover that the reason for their time - travel was not what they thought. Instead of going back to fix something, they were actually sent back to ensure that certain events happen. For instance, Naruto might think he's going back to save someone, but in reality, he needs to let that event occur for the future to be as it should be.
One possible main plot twist could be that they go back to a time when the Uchiha clan was not yet massacred. Sasuke might have the chance to prevent it, but this could have unforeseen consequences. For example, it could disrupt the balance of power in the ninja world at that time. Another plot twist could be that they go back to a time when Naruto's parents were alive. Naruto might get to meet them and learn from them directly, which would change his understanding of his own identity and power. A third plot twist could be that they find out that their time - traveling was actually part of a grand scheme by an ancient and powerful enemy, who wants to use their presence in the past to change the future in a way that benefits them.
One possible plot twist could be that their presence in the past changes the future in unexpected ways. For example, they might accidentally prevent some key events that led to their own growth and power. Maybe Naruto ends up changing the way he was treated as a child, which in turn affects his relationships with characters like Iruka and Sakura in the new future they are creating.
One possible plot twist could be that Dark Naruto tries to change the past to prevent his own dark transformation. He might attempt to save someone important who in the original timeline led him down the dark path. For example, if it was the death of a certain character that made him turn dark, he could go back and try to save that person. This would completely change the future and the Naruto we know from the original story.
A great plot twist could be related to the time - travel itself. What if the way time - travel works in the WW2 era is different from how it is in Harry's time? This could lead to him getting stuck or being unable to use his magic properly. Or perhaps he discovers that a certain event in WW2 was actually caused by a wizard from the future (not just him) who was trying to correct something in the wizarding world's past. His attempts to fix things could then make the situation even more complicated as he unknowingly steps on the toes of a much larger time - traveling plan.
One possible plot twist could be that their relationship is a cover for a secret mission. They pretend to be dating to get close to an enemy who is targeting couples. So while they seem to be having normal dates, they are actually gathering intel.
Well, perhaps a plot twist could be that when Kirito goes back in time, he discovers that his own existence in the past was a key factor in creating the problems he faced in the future. So, he has to figure out a way to change things without erasing himself. Or, he could go back and find that the person he loves in his original timeline has a completely different personality or role in the past, which throws him off and makes his feelings really complicated.
One possible main plot could be Naruto using his Anbu skills to change the past. Maybe he tries to prevent certain tragedies like the Uchiha massacre. He could secretly influence events, using his knowledge of the future and his combat abilities.
One possible main plot could be that Naruto and Kakashi go back in time to prevent a great disaster. For example, they might aim to stop the Nine - Tailed Fox attack on Konoha that happened in the past. This would involve them having to deal with different versions of their friends and enemies. They would need to be careful not to change too much of the past, as it could have unforeseen consequences on the future they came from.
Well, one possible plot twist could be that Ino's perception is actually a misinterpretation. Maybe Naruto is just showing friendly admiration for Sasuke, but Ino mistakes it for being a 'fan' in a more extreme sense. For example, Naruto might be trying to bring Sasuke back to the village and Ino misreads his determination as fangirl - like behavior towards Sasuke.
Well, one plot twist could be that Naruto is actually using a new, secret jutsu that he's been developing in secret. This jutsu gives him an edge over Sasuke that Sasuke didn't expect. Another could be that Sasuke is actually holding back for some reason, like he doesn't really want to fight Naruto but Naruto misinterprets it as Sasuke being cocky and goes all out.
A plot twist might be that when Luke goes back in time, he finds out that the Force has a different set of rules in the past. This could lead to him having to relearn how to use the Force in this new 'historical' context. He could also meet characters that were thought to be long dead in his time, and these characters could either be allies or enemies. For instance, he might encounter an ancient Sith Lord who was thought to be only a legend. This would create a whole new set of challenges for Luke as he tries to find his way back to his own time while dealing with this unexpected threat.