I think Bakugo could be a character who time travels. He's extremely competitive and always wants to be the best. He might go back in time to outdo his rivals even more. For example, he could go back to his school days and show off his quirk in an even more impressive way. He might also go back to the time when he and Midoriya first had their conflict and handle it differently.
All Might might time travel in a fanfic. He could go back to his healthier days to relive his glory moments or to try and prevent his own decline. Maybe he wants to change something in his past that led to his current weakened state. He could also use the knowledge from the future to better train Midoriya from the very beginning.
Midoriya would be a likely candidate. He's always looking for ways to improve and become a better hero. Time travel could give him the chance to learn from past heroes directly, like All Might in his prime. He could also go back to understand more about One for All's past users and how to master the quirk faster.
Eleven could be a likely candidate. Given her powerful psychic abilities, she might accidentally or purposefully time travel. Her powers have always been a bit unpredictable, and time travel could be an extension of that. She has a strong connection to the Upside Down, so she might be sent back in time to learn more about its origin or how to stop it.
Teresa could also be a likely one. She has a special connection to the whole situation, being part of the experiment in a different way. She might time travel to understand more about her own role and to try to make amends for some of the things she did under the control of WICKED. She could go back to change how she interacted with Thomas and the others in the early days, hoping to create a better outcome for everyone.
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.
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.
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.
Starlight Glimmer also has a good chance. She has shown great aptitude for complex magic. After her reform, she could be on a journey of self - discovery and exploration. Time travel could be a part of that as she tries to understand the past mistakes and how to prevent similar things from happening in the future. And she has the determination to master such a difficult magic.
One popular trope is the 'fix - it' time travel. This is where a character goes back in time to fix a major event that went wrong in the original timeline, like preventing a hero's death. Another is the 'fish - out - of - water' trope. When a character travels to a different time period, they have to adapt to the new ways and rules. For example, if a modern - day hero travels back to the early days of quirks, they'd find a very different society. There's also the 'time - loop' trope, where a character is stuck repeating the same period of time until they figure out how to break the loop.
I think Zoro would be really interesting to time travel. He has a strong sense of honor and his swordsmanship skills are top - notch. If he traveled to the past, he could learn from the greatest swordsmen of that era and bring back ancient sword techniques to the present. In the future, he could see how swordsmanship has evolved and maybe even find a way to further enhance his own skills.
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.