I think Todoroki would be fascinating. Going back in time could give him the opportunity to prevent the family issues that haunted him. He could try to save his mother from the mental breakdown and also change his relationship with his father at an earlier stage, which would completely reshape his character and his quirk development.
Bakugo could also be a great choice. If he went back in time, he might have to face his own arrogance from the past and try to change his ways earlier. It could be a journey of self - discovery for him as he realizes how his actions in the past affected others and how he can be a better person and hero in the future.
Hinata would be a great choice. He's so full of energy and determination. If he traveled back in time, he could share his experiences of playing against strong opponents like Nekoma and Aoba Johsai with his younger self. It would be really cool to see how his past self would react and grow even faster with that knowledge.
Hook would be an interesting character for OUAT time travel fanfiction. His past as a pirate and his relationship with Rumplestiltskin are full of drama. If he were to time travel, he could go back to when he first lost his hand to Rumplestiltskin and try to change that event. Or he could travel to a time when he was a more ruthless pirate and see how that version of himself compares to the man he has become.
Kazama Chikage might be an interesting choice as well. He is a powerful and somewhat arrogant character. If he time - travels, perhaps to a past era where his clan was even more powerful, he could try to change history to make his clan even more dominant. Or if he travels to a future where his power is nothing compared to modern technology, his struggle to come to terms with his new position in the world would be an interesting plotline.
Iroh would be fascinating to see time - traveling. He has so much wisdom already. If he traveled to different times, he could share his knowledge and perhaps change some key events. He could also gain more insights from other time periods, which would further enrich his already deep understanding of the world.
Definitely Iona. As an advanced Fog ship that has developed emotions and a sense of self, if she were to time travel, she could have a very unique perspective. She might be confused by the differences in the past or future she travels to, and her attempts to understand and fit in could lead to some really engaging storylines. Also, her relationship with the other characters would be very different in a time - travel context.
Lip would be really interesting. He's smart but has his own set of problems. If he could time - travel, he might go back to fix some of his mistakes, like not taking better care of Fiona or making better choices in his relationships. He could use his intelligence to change things for the better in the past.
Daenerys Targaryen. She has a strong will and a mission to claim the Iron Throne. If she time - traveled, she could meet her ancestors and learn from their successes and failures. She could also try to prevent the downfall of her family in the past, which would have a huge impact on the present state of Westeros in the fanfiction world.
I think Izuku Midoriya would be really interesting. He's the main character and has so much knowledge about the heroes and villains. If he time - travels, he could use his understanding of quirks and combat strategies to change the past or future in significant ways. For example, he could go back and give advice to All Might when he was younger, which might change how All Might deals with villains later on.
Ahsoka Tano would be a great choice. She has a complex history within the Clone Wars. If she were to travel back in time, she could interact with her younger self. She might be able to pass on wisdom she gained from her later experiences, like how to better handle the politics within the Jedi Order and the Galactic Republic.
Wei Wuxian would be very interesting. He has such a complex character arc in the original story. If he were to travel through time, say, back to a time before his fall from grace, he could potentially change things for the better. He could use his knowledge of the future to avoid certain tragedies, or he could interact with his past self in a really unique way, like giving advice or just seeing how much he has changed.