Obviously, Goku would be a main character he'd interact with. If he goes back to when Goku was a kid, he could train with him, or try to convince Goku's grandpa to let him train Goku in a different way. Another character would be Bulma. If he goes back far enough, he could meet a younger Bulma and perhaps change their relationship dynamics. He might also interact with his younger self. This could lead to some really interesting self - reflection and growth as he tries to guide his younger, more hot - headed self.
In some 'Vegeta goes back in time' fanfictions, Vegeta might go back to the time when the Saiyans were still under the rule of King Vegeta. He could try to change the Saiyan culture from being so war - like and brutal. He might introduce new ways of thinking and training that would not only make the Saiyans stronger but also more united. This could lead to a completely different future for the Saiyans, where they don't get wiped out by Frieza and instead become a more dominant force in the universe. He could also form different alliances with other races much earlier, which would change the power dynamics in the galaxy.
She could meet her younger self. This would be an interesting encounter as she could offer advice and guidance to her younger version. Maybe she could help her younger self to be less afraid of her powers.
In fanfiction, if Goku and Vegeta go back in time, they might change the course of history. For example, they could prevent some of the villains from ever becoming powerful. They may also meet their past selves, which could lead to some really interesting battles or training sessions. And they could introduce new techniques to their past counterparts, making the Saiyans even stronger earlier in the timeline.
Well, they could change the entire timeline. Maybe they'd go back and team up with their younger selves to take on foes that were previously too powerful. They might also influence the relationships between characters. For instance, Vegeta could potentially have a different attitude towards the Z - fighters earlier, which would change the dynamics of their group. It could lead to a whole new set of adventures and battles that we haven't seen in the original story.
He could change the course of major events. For example, he might prevent the rise of a powerful villain. This would have a huge impact on the entire galaxy. Maybe he could save some characters who died in the original timeline.
One interesting aspect could be that Luke goes back to a time when the Sith were just emerging. He could try to root out the Sith threat before it became as powerful as it did. He might have to be very careful not to disrupt the timeline too much, but his Jedi wisdom could be a great asset in this time - traveling adventure.
In this fanfiction, Sora might change key events. Maybe he could prevent some of the tragedies that occurred in the original story. For example, he could save a character who was lost before.
One possible plot could be that Kagome goes back in time and tries to change a major event in the past. For example, she might try to prevent a big battle that had a lot of casualties. She could use her modern knowledge and skills to her advantage in the past, like using first - aid knowledge to save lives.