Harry Potter is the central figure. However, in 'death sends harry back in time fanfiction', characters from the past can also become main characters in a sense. For example, Harry's parents, James and Lily. Harry might interact with them in ways he never could before. Bellatrix Lestrange could also be a key character if Harry decides to target the Death Eaters earlier. And then there are the Hogwarts professors like McGonagall who could play important roles in Harry's new journey through time.
The main character is Harry, no doubt. But other characters like Snape can become more prominent in this type of fanfiction. Snape's complex relationship with Harry could be explored in new ways if Harry goes back in time. Sirius Black could also be a major character. Harry might try to save Sirius earlier or change the way their relationship developed. And of course, Voldemort remains an important character as Harry's main adversary, and Harry may try to defeat him in a different way this time around.
Obviously, Harry Potter is the main character. He is the one being sent back in time after all. Dumbledore often plays a significant role too. Since he was such an important figure in Harry's life, he might be the one to guide Harry in the new timeline. Hermione and Ron are also likely to be important. They were Harry's closest friends, and in the time - travel scenario, Harry might try to involve them in his new plans early on.
One interesting plot could be that Harry goes back in time and uses his future knowledge to prevent certain tragedies. For example, he might be able to save some characters who died in the original timeline. Another plot could involve him changing the relationships he had in the past. Maybe he could befriend those he was once enemies with or vice versa. He could also use his knowledge of magic from the future to outwit his past enemies in new and unexpected ways.
Sometimes, there could be historical characters as main characters too. For instance, if Nero travels back to the Roman Empire, Caesar or Cleopatra could be important characters. They would interact with Nero, and their different personalities and goals would create interesting storylines. Nero might have to work with them or against them depending on the plot.
Obviously, Harry is the main character. He's the one going back in time. Then there are the Marauders - James Potter, Sirius Black, Remus Lupin, and Peter Pettigrew. Lily Evans, Harry's mother, also often plays a significant role as Harry might interact with her in the past. Dumbledore could be another important character, as he might be aware of Harry's time - traveling or be involved in some way in the events that occur in the past.
Neville Longbottom can also be a main character in some 'Harry Potter goes back in time' fanfictions. Given his growth and importance in the original series, in the fanfic, Harry might go back and help Neville become more confident earlier. This could have a significant impact on the fight against Voldemort as Neville could then be an even more powerful ally from an earlier time.
Main characters Percy will interact with? Well, he'll surely have some sort of encounter with the Fates. Since time travel is involved, the Fates would have a role to play. Maybe he has to convince them not to interfere too much with the changes he's making. Also, he could interact with the Titans in a more personal way. Not just as enemies as in his own time, but perhaps understand their motives better by being in the past with them. And don't forget about the minor gods. In the past, they might have had more influence or different relationships, and Percy could get caught up in all of that.
In a lot of these fanfictions, Luna Lovegood can be a key character. She has an open - minded and unique way of looking at things. So she might be the one who first suspects that Harry isn't really dead, or she could be part of the plan to help Harry fake his death and then communicate with him in some secret way while everyone else thinks he's gone.
Obviously, Naruto himself is the main character as he is the one sent back in time. Sasuke is also often involved as Naruto's relationship with him is a central part of the Naruto story. Kakashi could be involved too, as Naruto might seek his help or try to influence his training methods. Also, the various Hokages might be important characters as Naruto could interact with them in the past to change the course of events.
The main characters are Sam and Dean Winchester, of course. But in some fanfictions, Bobby Singer might also be involved. Since he was like a father figure to them, he could be the one guiding them through the time - travel process, or he could be there in the past waiting for them. Also, the characters of their parents, Mary and John Winchester, might show up if they go back to a time when their parents were alive.
It depends on the source material it's based on. But usually, the main characters from the original work will be prominent. For instance, if it's related to a fantasy series, the hero and the main antagonist from that series would likely be main characters in the fanfiction as well.
Well, clearly Harry is a main character as his name is in the title. As for the elves, we don't know exactly which elves will be in it. It could be some well - known elves from the Harry Potter universe like Dobby or Winky, or it could be entirely new elf characters created by the fanfiction author. There might also be other characters from the original Harry Potter series who interact with Harry during his time - traveling adventure related to the elves.