Well, of course, Ichigo himself is the central character. But Rukia also often plays an important role. Since she was the one who initially transferred her powers to Ichigo, in the time - travel scenarios, she might be involved in different ways. Maybe Ichigo goes back in time to save her from some danger she faced in the past.
It really depends on the source material. For example, if it's based on a superhero franchise, it could be the main superhero like Superman or Batman. If it's a fantasy - based one, perhaps a wizard or a chosen hero from the original work. There's no one - size - fits - all answer as different fanfictions can be based on different universes and thus feature different popular characters.
Obviously, Severus Snape is the central character. He is the one who travels back in time, so all the actions and changes are centered around him. But other important characters often include Lily Evans. Since Snape had a deep connection with her, he might try to interact with her in different ways to change the past.
Obviously, Harry himself is the central character. Hermione is also often involved as she is Harry's friend. Ron too, as they are a trio. Dumbledore usually plays an important role as he is the headmaster. Snape is also a popular character in these fanfictions as Harry might try to change their relationship. And of course, Hagrid, who is always there for Harry in the original story and could be involved in new and different ways in the fanfiction.
Sasuke is also a popular choice. Given his complex character and his quest for power, in a time - travel scenario, he could go back in time to gain more power or change the events that led to the downfall of his clan. Another character is Kakashi. His past and his relationship with Obito could be explored in a time - travel fanfiction. He could try to prevent Obito's fall to the dark side if he had the power to time - travel.
King might also be a character in time travel fanfiction. His search for his true identity could be further explored through time travel. He could go back to the time when his species was more prevalent in the Boiling Isles to learn about his origins, which would be an exciting adventure in the context of time travel fanfiction.
Well, in many izuku goes back in time fanfictions, besides Izuku himself, his mother is an important character. He might go back in time to be a better son, protect her more, or even change things that affected her in the past. Another often - seen character is Aizawa. As Izuku's teacher, Izuku could use his time - travel knowledge to impress Aizawa earlier or get more help from him in his hero training. And of course, the villains like Shigaraki could also be involved. Izuku might try to stop Shigaraki from becoming a villain by going back in time and changing certain events that led to his fall.
Naruto himself is obviously very popular in these fanfictions as the main character. His decisions are the central focus. Sasuke is also commonly involved. Since Sasuke's actions and decisions often intertwine with Naruto's, fanfiction writers like to explore how different decisions from Naruto would affect Sasuke's path. For example, if Naruto made a decision that could sway Sasuke from his revenge - seeking journey.
Naruto is often involved. Since he has the ability to transform into the Nine - Tails in the original series, fanfiction might expand on this by giving him more shapeshifting abilities or different forms of the Nine - Tails transformation. For example, a more powerful and controlled version of the full - Nine - Tails form.
Edward and Bella from 'Twilight' are often used in difficult love fanfiction. Their relationship has elements of danger and the struggle between Edward's vampire nature and Bella's human existence. Another pair could be Harry Potter and Hermione Granger. Some fanfictions explore a more romantic relationship between them, which is difficult considering their strong friendship and the overall plot of the original series.
Sasuke is often involved. His powerful chakra and skills make him a natural fit for stories involving barriers. He could be trying to break through a powerful barrier or using his Sharingan to analyze and then counter a barrier technique. Naruto is also popular. His large chakra reserves could be used to power up or break barriers in unique ways.