Another possibility is Kakashi. He has a wealth of knowledge and experience. He might time - travel to the Fourth Shinobi War to save his comrades who were lost. He could use his Sharingan and his strategic mind to change the course of the war. Also, his relationship with many of the key characters makes him a character who could have a significant impact if he were to travel back in time during that war.
Naruto himself could be a likely time - traveler. He has a strong sense of justice and a desire to protect his friends and the village. If he saw a way to go back in time and prevent the destruction and loss in the Fourth Shinobi War, he would probably take it. Plus, his chakra and determination might be what enables the time - travel in the first place.
Naruto himself could be a likely time traveler. He has a strong sense of justice and a desire to prevent tragedies. If he learned of a way to travel back in time to the clan wars, he would probably try to stop the bloodshed and promote peace among the clans. Another possibility is Sasuke. Given his past and his connection to the Uchiha clan, he might want to go back to the clan wars to change the fate of his clan, especially the massacre.
He would likely interact with his father, Minato. Since Minato was very active during the Third War, Naruto would have a lot to talk to him about, like his own experiences and the future. Another character would be Jiraiya. Jiraiya was also involved in the war and he was Naruto's mentor, so Naruto would surely seek him out. And of course, he might interact with the Third Hokage as well, to gain more knowledge about the past and how to handle the situation in the war.
Maybe in the fanfiction, the time travel causes a mix - up of jutsu knowledge. A character from the future accidentally gives the wrong kind of jutsu knowledge to a past - self or another character during the Fourth Shinobi War. This then leads to new and unforeseen strategies being developed by the shinobi, either for good or bad, depending on how it's used. It could completely change the power dynamics in the war.
Naruto is a very likely character. Given his strong will and connection to the Nine - Tails, he would be motivated to time - travel to fix problems related to the Juubi. His ability to make friends and influence people would also play a big role in any time - traveling story.
I think Yamato could be a good choice too. His ability to control wood style could be really useful in the past. Maybe he could time - travel to help with the growth of the first trees in the ninja world or something like that. And his calm and collected nature would help him adapt to the new situation in the past.
Ban could be another one. He has his own backstory related to the sins and his immortality. He might time travel to find a way to break free from his immortality curse or to go back and correct a mistake he made when he was under the influence of one of the sins, like greed when he stole something important in the past.
Star - Lord is a likely candidate. He's always been a bit of a risk - taker and his curiosity might lead him to experiment with time travel technology.
I think Fundy would be likely to time travel. He has a complex relationship with his family and the SMP. Time travel could be a means for him to understand his father better or change the way his family relationships developed. GeorgeNotFound could also be a candidate. He's often in the background but has a strong connection to Dream. Time travel might be his way of getting more involved in the SMP's events and helping Dream in a different way. Lastly, Niki could be a time traveler. She has been through a lot of changes on the SMP, and time travel could be her opportunity to go back and make the SMP a more inclusive and friendly place from the start, especially for those who have been marginalized.
One popular original character might be a young, prodigious shinobi from a small village. They have unique abilities that set them apart, like the power to control the elements in a completely new way. Another could be a mysterious figure who shows up during the war and has a connection to an ancient shinobi clan that was thought to be extinct. And then there's the brave female shinobi who defies gender norms and becomes a respected leader on the battlefield.
One great Naruto Third Shinobi War time travel fanfiction is 'Back to the War'. It has an interesting plot where the main character goes back in time and tries to change the outcome of the war. The character development is well - done and it stays true to the Naruto universe's lore.