All Might might also be a key character. His influence on Izuku and the hero world is huge. In a future - past scenario, he could be a source of wisdom and power, perhaps even having some hidden knowledge about the events that led to the bad future. And his relationship with Izuku in this different timeline could be explored more deeply.
Katsuki Bakugo could also be a main character. His rivalry with Izuku is a major part of the series. In this fanfiction, he might be forced to work with Izuku more closely than ever to prevent the future from happening. His explosive quirk could be very useful in combat situations in the past as they face off against the threats that will lead to the future they want to avoid.
Definitely Izuku Midoriya. He's the main protagonist in the original series, so he would probably play a crucial role in any 'Days of Future Past' type of story. He could be the one leading the charge to change the future.
Another possibility is that the fanfiction explores the powers of the characters in a new light. Since they are in a different time period, they might have to use their quirks in unexpected ways. Maybe some quirks are more or less effective in the past compared to the present, and this creates new challenges and strategies for the heroes as they try to change the future.
It could be Deku's son or daughter. They would inherit some of his amazing quirk, but also face the pressure of living up to their father's legacy. They would have to carve their own path in the hero world.
Obviously, Izuku Midoriya will be the central character. His friends from U.A. High like Ochaco Uraraka and Tenya Iida are likely to be involved. They would be there to support or oppose Izuku depending on the nature of the spiral he's in. Also, All Might might play a role as Izuku's mentor, guiding him through whatever challenges the spiral presents.
Typical main characters in such a story could be Wolverine, as he is often central in X - Men stories. And there might be Professor X and Magneto as well, since they are key figures in the mutant world.
I think the students like Kaminari and Sero would be involved. Kaminari with his goofy personality might initiate some pranks, and Sero could use his tape quirk to set up some elaborate prank setups. Also, the teachers like Aizawa could be involved. He might play a prank on the students to teach them a lesson in a rather unorthodox way. Another character could be Todoroki. His rather stoic nature could be a great contrast to the chaos of a prank.
In a darker take, even some of the younger students at U.A. High could die. This would be a very emotional and impactful event. It would show the harsh reality of the hero world and how not everyone is guaranteed to survive, no matter how much potential they have.
Obviously, Naruto would be the main character since it's about his past seeing the future. Sasuke would also be important as Naruto's relationship with him is central to the Naruto series. Kakashi too, as he is Naruto's teacher and mentor, and his guidance might be influenced by Naruto's new - found knowledge of the future.
I think Icarus is the central figure in this fanfiction. But characters like Midoriya Izuku would also be important. Izuku's journey as a hero - in - training could be intertwined with Icarus'. Maybe they become friends or rivals. And villains from My Hero Academia, such as Tomura Shigaraki, could also be main characters. His evil plans might be affected by or target Icarus, adding more drama to the story.
Definitely Todoroki. His ice and fire powers could be used in different ways against Godzilla. He could try to freeze parts of Godzilla to immobilize it or use his fire to counter any heat - based attacks Godzilla might have. Also, Recovery Girl could be involved in an interesting way. After any battles with Godzilla, she would be needed to heal the injured heroes, and she might also come up with some unique medical strategies based on Godzilla's physiology if she could study it.
Definitely Deku. His determination and continuous growth would make him stand out in college. He'd probably be at the top of his classes, always eager to learn more about quirks and heroics. Bakugo would also shine. His powerful quirk and competitive nature would lead to some intense rivalries and great character development in a college environment. And Todoroki, with his complex family background and dual - natured quirk, would have a lot of room for exploration in college as he tries to further master his powers and come to terms with his past.