Harry Potter himself is often a main character. He might use the time travel necklace to gain more knowledge about his parents or to find a way to defeat Voldemort more effectively.
Ron Weasley can also be a main character in such fanfiction. His loyalty to Harry and his own experiences in the original story can add depth to the time - travel redo plot. He could be the one to provide emotional support or come up with unexpected solutions during the time - travel adventures, even if he may not be as well - versed in the technicalities of magic as Hermione.
In some fanfictions, other important characters from the original series like Hermione Granger or Ron Weasley could also be involved. They might help the founders understand the modern world or play a role in the events that unfold during the time - traveling escapades. For example, Hermione's vast knowledge of magic could be useful in deciphering ancient spells that the founders use.
Well, Inuyasha and Kagome are almost always involved. They are the central characters of the original series, so it's natural for them to be in time travel fanfictions. Kagome is the one who can travel through the well between her time and Inuyasha's time in the original story, so she often plays a key role in any time - travel - related plot. Inuyasha, with his half - demon powers and his connection to the past of the feudal era, is also crucial.
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.
Obviously, Harry Potter himself is the central character as it's about him in diapers. Dumbledore often features as he plays a crucial role in Harry's life. Hagrid might also be there as he has a special connection with Harry. And of course, the Dursleys could be part of the story, perhaps in their begrudging care of baby Harry.
Obviously, the main members of Team Natsu like Natsu, Lucy, Gray, Erza, and Happy are always involved. They are the core of the group and any time travel adventure usually revolves around them.
Naruto is usually one of the main characters. After all, it's a Naruto - centered fanfiction. Sasuke might also be involved as he is a central figure in the Naruto series. Sakura could be there too, given her importance in the original story. And sometimes, characters like Kakashi or Jiraiya might be part of the time - traveling group, as they are strong and experienced ninjas who can add depth to the story.
Obviously, Kushina herself is the central character. But often, Minato, her husband, is also involved. Since they are closely related, his actions and reactions to Kushina's time - traveling situation are important parts of the story. Naruto can also be a key character. If Kushina travels to a time when Naruto is already born or in the future, their interactions can be very emotional and drive the plot forward.
Obviously, Harry Potter himself is often a central figure. His friends like Ron Weasley and Hermione Granger also play important roles as they are part of his extended family - like group. Ginny Weasley, as Harry's wife in the original series, is also a key character. Then there are the older generation characters such as Molly and Arthur Weasley who bring their wisdom and family values to the alliance.
Obviously, Tonks is the central character. Her husband, Lupin, is also a very important figure. Harry Potter and his friends might also be involved in some way. For example, they could offer support or protection to Tonks during her pregnancy. Hermione, with her vast knowledge of magic, might be helping Tonks with any magical complications related to the pregnancy.