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.
A really interesting plot twist could be that Kirito goes back in time and finds that the virtual world he thought was unique to his own time actually had a much older origin. He might stumble upon an ancient civilization within the virtual world that was lost in time. This discovery could lead to him having to learn new skills and knowledge from this ancient group to be able to change the future for the better. Maybe they have a different way of fighting the digital threats that he can bring back to his own time.
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.
One possible plot twist could be that when they go back in time, they accidentally change a small event that has huge consequences in the present. For example, they might prevent a meeting between two people that was crucial for the formation of a powerful coven, and now they have to figure out how to fix it before they return to their own time.
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 plot twist could be that they end up in the wrong time period completely. Instead of the time they intended to go to, they land in a much earlier era of magic. There, they discover secrets about magic that have been long forgotten in their time. However, they also face the danger of getting stuck there because the magic that sent them back was calibrated for a different time, and they have to find a way to adapt it to return home.
A possible plot twist is that Kakashi goes back in time and finds out that the events he thought were true in the past were actually misinformation. This could completely change his perception of the history of the ninja world and his own role in it. Also, he might go back to a time when Orochimaru was just starting his dark experiments. Kakashi could try to stop Orochimaru right from the start, but in doing so, he might end up creating new villains or problems. Or perhaps, when he travels back, he loses some of his memories from the future, which makes it difficult for him to use his knowledge effectively to change things.
A great plot twist could be that Darth Vader travels back to the time when the Jedi Order was at its peak. His dark side presence is detected by the Jedi Council immediately. However, instead of being able to simply capture or kill him, they find that his knowledge of future events gives him an edge. He might use this to manipulate the Jedi, creating internal strife within the Order. This could also lead to some Jedi being tempted by the dark side because of the power that Vader represents. And all of this could ultimately reshape the future of the galaxy far more than anyone expected.
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 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 interesting plot twist could be that when they go back in time, they accidentally change a small event that has huge ramifications in the future. For example, they might prevent a key Hollow attack that was originally supposed to happen. This would then change the relationships between characters. Maybe Ichigo doesn't meet some of his friends in the same way because that Hollow attack was a catalyst for many things in the original timeline. Another plot twist could be that they find out there's a hidden force that has been manipulating time all along and they have to fight against it to set things right. And a third could be that when they go back, they discover that their own powers work differently in the past, which adds a whole new layer of challenges for them to overcome.
One possible plotline could be that Noctis goes back in time to prevent the fall of his kingdom. He could use his knowledge of the future to stop the events that led to its destruction. For example, he might prevent the betrayal of a key ally or stop the spread of a deadly plague that weakened the kingdom. Another plotline could be that Noctis goes back to a time when his father was still alive. He could then learn more about his father's rule and gain valuable advice on how to be a better king. Or perhaps he goes back in time to change a personal decision that had far - reaching consequences, like a choice he made about a relationship that affected his leadership later on.