Jon Snow would be a likely candidate. Given his complex story arc and his role in the fight against the White Walkers, a time loop could give him the chance to make different decisions and potentially save more lives. He could also use the loop to better understand his true identity and his place in the world.
Daenerys Targaryen is another. With her dragons and her quest for the Iron Throne, a time loop could allow her to strategize more effectively. She might be able to avoid some of the mistakes she made in her original journey, like the decisions that led to her downfall in the later parts of the story.
Jiraiya could also be involved. Picture him writing his 'Make - Out - Paradise' books while stuck in a time loop. He might keep getting interrupted by Naruto or other characters in different and humorous ways each time the loop resets, like having his ink spilled or his notes stolen by a curious Naruto.
Sasuke could also be a character who breaks the time loop. He is highly intelligent and has a thirst for power and knowledge. If he realizes that he is in a time loop, he would likely be very intrigued and start investigating. His Sharingan might give him some insights into the nature of the loop and help him find a way to break it.
Well, Arya Stark has a good chance. She's highly adaptable and has been through so much. Her skills as a Faceless Man could potentially be used to discover the secrets of the time loop and break it. Also, Jon Snow. He has a special connection to the North and has faced death and come back. His unique position and the respect he commands could help him find a way to end the time loop. And then there's Tyrion Lannister. His intelligence and ability to think outside the box might lead him to the solution to break the loop.
Katsuki Bakugo, with his powerful quirk and complex personality, could be a character in time travel fanfics. He might go back in time to prove himself even more or to change certain interactions he had with other characters in the past.
Lelouch is a very likely candidate. Given his intelligence and his desire to change the world, time travel could be a means for him to correct past mistakes or gain more power to overthrow Britannia. Another one could be Suzaku. He has a strong sense of justice and might use time travel to prevent some of the tragedies that occurred.
Definitely Hinata. Her gentle yet strong - willed nature could be an interesting contrast when dealing with the often - mischievous yokai from Nurarihyon. Gaara too, as his own experiences with being an outcast and having a powerful force within him could have parallels in the Nurarihyon world where some yokai are feared or misunderstood. And Rock Lee, his determination and unique fighting style could bring a new dynamic to the interactions in the fanfic.
Time - turners are important in time travel in the Harry Potter universe, and so the characters associated with them could be involved. For example, Hermione, who was given a Time - Turner in the original story. But also, characters like Fred and George Weasley could be interesting inclusions. They are creative and mischievous, and they might come up with unique ways to use time travel to fix things. Maybe they could use their Weasley's Wizard Wheezes products in conjunction with time travel to make things right.
Another concept is the exploration of character development within the loop. A character might learn from their mistakes in previous loops and grow in unexpected ways. They could gain new skills or knowledge that they use to their advantage. For instance, a character could learn how to better handle dragons or deal with the White Walkers.
Shinji is a very likely character. His complex relationship with his father and his role as the main pilot make him a prime candidate for time travel scenarios. He could go back in time to try and fix things or understand his father better.
Jon Snow is often a popular choice. His mysterious parentage and his role in the story make him an interesting character to time - travel. People like to explore how his knowledge of future events could change his actions and the fate of the Seven Kingdoms. Daenerys Targaryen is also popular. Her journey to claim the Iron Throne could be drastically altered with time travel knowledge.