His classmates like Bakugo could be a main character. Bakugo might be one of the first to notice the strange changes in Izuku and could be both scared and angry about it. He might try to confront Izuku, which could lead to some intense scenes.
His friends from U.A. High School such as Bakugo, Ochaco, and Iida would also likely be main characters. Since Izuku is scaring everyone, they would be the ones experiencing the fear and trying to figure out what has happened to him. Their reactions and attempts to deal with the situation would be important parts of the story.
One possible plot could be that Izuku has been through a really traumatic experience that has changed him. He starts to isolate himself and when people try to approach him, he acts in a way that scares them off. He could have developed some sort of survival - based aggression. For instance, if he was trapped in a really dangerous situation where he had to fight to survive, he might now react harshly to any sudden movements or people getting too close to him, which would scare his friends and classmates.
There could be his friends like Ochaco Uraraka. She might be in a position where she's trying to understand Izuku's situation and help him. Maybe she tries to convince the people forcing Izuku to give him some space.
Perhaps in the fanfic, Izuku is possessed by some dark entity which changes his behavior and makes him do terrifying things, causing fear among his friends and foes alike. For example, his actions might be unpredictable and seem dangerous to those who know him. He could start speaking in strange voices or have sudden outbursts of strange powers that startle everyone. This would lead to a situation where everyone is scared of him, and the story could revolve around how he tries to get rid of this possession or control this new and scary side of himself.
One could be All Might. Even if Izuku leaves Japan, All Might might still be in contact with him, guiding him from afar. Another could be Bakugo. Their relationship is complex, and Bakugo might have some sort of reaction to Izuku leaving, perhaps feeling a sense of rivalry still and trying to prove he can be a great hero in Japan while Izuku is away.
There could be other U.A. teachers like All Might. He might play a role in Izuku's development even though Midnight has adopted him. Another character could be Bakugo. His relationship with Izuku could change or be explored further in this fanfiction.
All Might would probably be in it. Since he's Izuku's mentor, he could play a role in helping Izuku understand and control his time - controlling power. Maybe he has some past experience related to time powers that he shares with Izuku.
Definitely his friends from U.A. High. Bakugo would be an interesting character in this scenario. He might initially be annoyed but then develop a soft spot for baby Izuku. Ochaco would also be there, using her quirk in creative ways to take care of him, like floating toys to keep him entertained.
Well, in many izuku goes back in time fanfictions, besides Izuku himself, his mother is an important character. He might go back in time to be a better son, protect her more, or even change things that affected her in the past. Another often - seen character is Aizawa. As Izuku's teacher, Izuku could use his time - travel knowledge to impress Aizawa earlier or get more help from him in his hero training. And of course, the villains like Shigaraki could also be involved. Izuku might try to stop Shigaraki from becoming a villain by going back in time and changing certain events that led to his fall.
Obviously, Izuku is one of the main characters since the title mentions him. He's the demigod in this fanfiction.