Another possible main character could be a historian or a scholar within the order. Their knowledge of the past could be crucial in helping the order navigate the historical period they travel to, and they might also be on a personal quest to discover something that has been lost in time.
One interesting concept could be how the characters adapt to the past's different social norms. For example, if they come from a more modern time, they might struggle with the lack of certain technologies or the strict moral codes of the past era.
Well, perhaps the members of the order find themselves in a future where their magic has evolved in unexpected ways. They might encounter new enemies or challenges that are based on futuristic technology that they have to adapt to using their magical skills.
There could be a combination of old and new members. The old members with their deep knowledge of the order's history and magic, and the new members with their adaptability. Together, they can face the challenges of the future, learn from each other, and perhaps change the future as well as the order itself for the better.
He might accidentally change the future. For example, he could prevent important events from occurring that were crucial for the development of the present he came from. Maybe he meets his parents at a younger age and reveals too much about the future, which could cause them to make different decisions.
In such a fanfiction, Naruto might try to prevent some of the tragedies that occurred in the past. For example, he could stop the Uchiha massacre. He would use his knowledge from the future to change things. Maybe he'd also be able to save some characters who died early in the original story, like Jiraiya. And he could potentially have a huge impact on the relationships between different clans, as he'd know about future conflicts.
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.
Well, in a fanfiction where Naruto travels to the past, he could meet his parents when they were young. He could also learn new jutsu from the past ninjas that were lost over time. Maybe he'd even be able to influence the early development of the Hidden Leaf Village in ways that would make it stronger in his own time.
Another option is a jealous individual from Sakura's own time who somehow manages to follow her into the past. This person is envious of Sakura and wants to take over her role in the past - time events. They would constantly try to undermine Sakura and take credit for her actions, causing a lot of trouble for her during her time - traveling adventure.
Obviously, Harry himself is a common character. Hermione is also often included as she is Harry's closest friend and very intelligent, so she can help Harry figure out how to navigate the past. Ron might be there too, providing some comic relief and loyalty. Dumbledore usually makes an appearance as he has a lot of knowledge and can offer guidance to Harry in the past.