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.
Luke could also go back to meet his father, Anakin, when he was still a young boy. He could be like a mentor to him, teaching him about the Force in a different way. This might prevent Anakin from ever turning to the dark side, which would rewrite the entire Star Wars story. He could introduce Anakin to different ways of using the Force that are more positive and less focused on power and control.
One idea could be Luke traveling back in time to the Clone Wars era. He could meet his father, Anakin Skywalker, before his fall to the Dark Side and try to prevent it. Maybe he uses his Jedi skills to influence Anakin in a positive way, like teaching him some advanced Jedi techniques that could strengthen his connection to the Light Side.
One possible plot could be Master Chief going back to a time before the Covenant war. He could use his knowledge and skills to prevent certain events that led to the war. For example, he might stop the discovery of the Halo rings by the Covenant in the first place, which would change the entire future of the galaxy.
He could interact in a way that tries to prevent future tragedies. When he meets Anakin Skywalker before his fall, Luke could try to be a positive influence. He might share some of his Jedi wisdom with Anakin in a veiled way, hoping to steer him away from the Dark Side. With other characters like Yoda, Luke could seek more in - depth knowledge about the Force that was perhaps lost in his own time. He would have to be very diplomatic in his interactions to avoid causing chaos in the past.
He could meet Dr. Halsey when she was just starting her research on the Spartan program. Master Chief could give her some insights from the future, which might change the way the program is developed.
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.
His time - traveling could have a huge impact. If he changes something in the past, it could create a ripple effect. For instance, if he stops Anakin from turning to the Dark Side, the whole Sith - Jedi dynamic in the galaxy would be different. There might not be an Empire, and the Jedi Order could have thrived without the purge.
Well, they might prevent some great tragedies in the Star Wars universe. For example, they could stop Anakin from turning to the Dark Side. This would completely change the course of history in the galaxy.
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.
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.