When Rachel goes back in time, she may change the way the glee club competes. She has the knowledge of what worked and what didn't in her previous experience. So she could focus the club on different choreography, staging, or even the overall theme of their performances. This would not only change their competition results but also how the other characters view their place in the glee club.
Harry might be more protective of his friends in the new timeline. He has seen what can happen to them in the future, so he'll do everything he can to keep them safe. With Hermione, he could encourage her to pursue her interests more freely, knowing how important her knowledge and skills will be. And with Ron, he may try to boost his confidence from the start, so Ron doesn't feel overshadowed as he did in the original timeline.
Well, for Naruto and Sasuke, their relationship might become even stronger earlier. In the past, they could train together more and understand each other's pain from the start. Sakura might be more assertive in her relationship with Sasuke, as she has the knowledge of what will happen in the future. She could try to prevent Sasuke from going down a dark path right from the beginning. And among the other members of Konoha 12, they might form closer bonds as they rely on each other more in this strange new situation of being in the past.
The storyline would change significantly. Firstly, Lelouch would have the upper hand in terms of knowledge. He'd know who to trust and who not to trust right away. This would change the power dynamics in his relationships. For instance, he could expose the true nature of some of the Britannian nobles much earlier.
When they go back in time, they may encounter situations where they have to protect each other. This could be a big turning point in their relationship. Let's say they go back to a time when there were dark wizards targeting their families. They would have to put aside their differences and fight side by side. This could lead to a complete transformation of their relationship. Draco might realize that Harry is not his enemy and Harry could see that Draco is capable of loyalty and self - sacrifice. It would be a very different dynamic from their relationship in the original timeline.
Well, if Draco goes back in time, he might become more humble. Seeing the past and the mistakes his family has made or is about to make could make him less arrogant. He would realize that his pure - blood status doesn't give him the right to look down on others.
His Force abilities could be different. Maybe he would discover new aspects of the Force in the past that were lost in his original time. For example, he could learn ancient Force techniques that were forgotten over time.
One common plot development could be that Harry tries to prevent the events that led to his death in the first place. For example, he might focus on changing how he dealt with Voldemort. Another could be that he uses his knowledge of the future to form different relationships. He may be more cautious with some people and more open with others. He could also try to save the lives of those who died before, like Sirius or Dumbledore.
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.
The characters would be devastated. Kurt, being one of her closest friends, would probably be in shock at first. He might go through a period of denial, thinking it's all a cruel joke. Then he would break down and cry, remembering all the times they shared together, from their fashion debates to their duets. He would likely be the one to organize a proper memorial for her, making sure it was as grand as Rachel would have wanted.
In this fanfiction, we might witness the Starks trying to fix historical mistakes. For example, if there was an event in the past that led to a great loss for the Stark family, they could go back in time to try and prevent it. This would involve a lot of planning and risk - taking, as changing the past can have unforeseen consequences. They would have to weigh the benefits against the potential disasters that could occur.