One interesting plot could be Aizen traveling back in time to prevent his own downfall. He might use his knowledge of future events to outwit his enemies before they even become a threat. For example, he could manipulate the events that led to his discovery by the Soul Society, thus ensuring his continued rise to power undetected.
Another plot could involve Aizen traveling back to change the past of certain characters. He may try to turn his former allies into more powerful tools by altering their past traumas or experiences. This could create a whole new dynamic in the Bleach universe, with characters having different personalities and abilities due to Aizen's meddling.
He might become more empathetic. Seeing the past versions of characters he once used or manipulated could make him question his own motives. He could start to value relationships more, rather than just seeing people as pawns in his grand scheme. For example, he might try to protect characters he previously endangered during his time - traveling adventures.
In aizen time travel fanfiction, he could go back to a crucial moment in his own past, like his time as a student in the Soul Society Academy. He could then manipulate events to make himself even more powerful and respected from the very beginning. He might also time travel to the future to see the consequences of his actions and then come back to adjust his plans accordingly.
One interesting plot could be a character going back in time to prevent a certain card from being created, which then changes the whole Yu - Gi - Oh! tournament scene. For example, if the Blue - Eyes White Dragon card was never created, how would the power balance shift among duelists?
One interesting plot could be Superman traveling back in time to prevent the destruction of Krypton. He could use his powers to stop the cataclysmic events that led to its downfall. Maybe he tries to convince the Kryptonian council of the impending danger, but faces resistance as they don't believe him at first.
Another plot could be that they travel to a future time where music has evolved into something completely different. They struggle to understand the new forms of music but also bring back some of the old charm from their time, creating a unique blend that revolutionizes the future music scene.
Another plot might be Kratos traveling to a time in the future of his own world. He could see the consequences of his actions and how the world has changed. Maybe he discovers that his actions have led to a new threat emerging, and he has to figure out how to fix it. This would add a new layer of responsibility to his character.
Well, in some time travel Kakashi fanfictions, there's a plot where Kakashi goes back in time right after Obito's 'death'. He tries to save Obito in a different way, not just by taking his eye. He could change the whole course of events that led to the formation of Akatsuki and the many tragedies that followed. This would completely rewrite the story of Naruto in many ways.
One interesting plot could be Octavia traveling back in time to prevent the initial war on Earth. She might use her knowledge of future events to broker peace between the different factions. Another could be her traveling to the time before the Ark was built to see if there were other ways to solve the overpopulation problem without having to send people to the ground in such a dangerous way. And she could also time travel to a future version of the world to see what kind of society has been built after all the chaos on Earth in her original time.
In some pokemon time travel fanfiction, the main character travels to the future. There, they might find that Pokemon have evolved in unexpected ways, like having new types or abilities. They then have to adapt and figure out how to battle with these new forms of Pokemon.
One interesting plot could be a modern person traveling back to WW2 and using their knowledge of future technology to help the Allies in a covert way, like improving communication systems. Another could be a time traveler trying to prevent a particular tragic event during the war, such as the bombing of a certain city. And there might be a plot where the time traveler has to adapt to the harsh wartime conditions and forms unexpected friendships with soldiers on the front line.