The main characters would surely include Deku. Then there could be his classmates from U.A. High. Iida might be one of them, who could have a very formal reaction to Deku's new haircut. And then there could be a new character, like a street - artist who is inspired by Deku's new look and starts to create art based on him.
Well, in the fanfiction, Deku might get a new look that changes how others perceive him. Maybe his friends at U.A. High are really surprised by his new haircut and it could lead to some funny or heartwarming interactions.
In the 'deku gets turned into a child fanfiction', Deku is the main focus, but his friends like Uraraka and Iida would be key characters. Uraraka might be especially kind and motherly towards him. Iida could be strict in making sure Deku follows the right path. And villains like Shigaraki could see this as an opportunity to target Deku in a new way, so they would also be significant characters in this scenario.
It could be All For One. He's a powerful and menacing villain in the My Hero Academia universe. Since Kurogiri is saving Deku, All For One might be trying to target Deku for his own purposes, like stealing his quirk or using him as a pawn in his grand scheme to take over the hero society.
Ron could be a main character. He might be the first one to notice Hermione's new haircut. He could have a really strong reaction, like blushing because he suddenly finds her even more attractive with the new look. And their relationship could develop further because of this change in her appearance.
All Might is another character that is very likely to appear. As Deku's mentor, he has a big influence on him. He would be concerned about Deku's health in relation to his quirk. Recovery Girl, the school nurse, would also be an important character. She would be the one trying to diagnose and treat Deku's illness.
Well, obviously Deku in two forms - the younger and the older version are the main characters. The younger Deku is the one who is still growing and learning, while the older Deku has more experience.
Perhaps Thor could be involved too. He might accidentally bump into Sigyn after her haircut and be really surprised. His reaction could lead to some humorous or important interactions. For example, he could be so shocked that he says something silly, which then spreads around and becomes a topic of gossip among the other characters.
Well, in this fanfiction, Sigyn getting a haircut could be part of a bigger plot. For example, it could be related to a prophecy or a magical event. The haircut might give her some special power or make her a target. Maybe she cuts her long hair short and suddenly she can move more freely in a fight, or perhaps her new look attracts the attention of an important character who has a role to play in her destiny.
In a 'Hermione gets a haircut' fanfiction, perhaps Hermione cuts her hair as a form of rebellion. She's been feeling restricted by the expectations placed on her. So she chops off her long locks into a pixie cut. This new appearance catches Draco's attention in a different way. He starts to see her in a new light and they end up having some interesting interactions that they wouldn't have had before.
Well, maybe Bucky would finally start to feel like a new person. The haircut could be a symbol of his transformation, leaving behind his troubled past and embracing a new identity.