In some cases, it could be other time - traveling vampires or supernatural beings who have their own agendas. They might not want Bella to interfere with the past as it could disrupt their own plans or power bases. These antagonists could be more shadowy figures, working behind the scenes to thwart Bella's efforts.
She could meet soldiers coming back from World War I. These soldiers would have their own stories of war and survival, and Bella might be drawn into their tales.
One idea could be that Bella travels back to a time when vampires first emerged. She could try to change the history of vampire - human relations, maybe prevent some of the early vampire - made disasters. Another idea is she goes back to a time in her own family's history and discovers secrets that shape her present. For example, she might find out that her family has some hidden connection to the supernatural world long before she became involved with Edward.
She could experience the historical events of 1918 first - hand. It was a time of great change. There were things like the end of World War I and the start of the Spanish Flu pandemic. Bella would be in the middle of all that chaos or transformation.
One great fanfiction could be where Bella travels back and she and Jasper form an unexpected alliance against the Volturi. They use their combined knowledge of the future and Jasper's combat skills to change the fate of the Cullen family.
She could meet the founders of Hogwarts. Imagine Hermione having a conversation with Rowena Ravenclaw about the importance of knowledge and wisdom. She might also meet Godric Gryffindor and learn about the true meaning of courage from him. Another person she could meet is Salazar Slytherin. It would be very interesting to see how she would interact with him, given his views on blood purity.
She could change the future of the Cullen family. Maybe she stops a certain event from happening that would have led to their downfall in the original timeline.
In some cases, the antagonist could be Esme herself, or rather a version of her from the past. The past Esme might be more naive or self - centered and not understand the implications of Esme's actions in the past. The present Esme is trying to make positive changes, but the past version of herself keeps getting in the way, either through her own actions or by influencing the people around her in a negative way.
One possible plot could be that Esme travels back to a time when she was about to make a crucial life decision. For example, she might go back to the moment before she met her significant other. In the past, she could then have the chance to see things from a different perspective. Maybe she realizes that the decision she made back then was actually the best one, or she might find out new things about herself or the people around her that she didn't know before, which could lead to a whole new set of adventures and self - discovery in the past and ultimately change her view of her present life.
One common theme is redemption. Percy often goes back in time to correct past mistakes, either his own or those of others, seeking a kind of redemption. For example, in some stories, he tries to save characters who died in the original timeline. Another theme is self - discovery. When he's in a different time, Percy learns more about himself and his powers. He might discover new abilities or a different side of his personality.