Maybe the fanfiction could focus on Eri's growth under Izuku's care. She starts to see herself as a normal girl with a powerful quirk, not just a tool. Izuku helps her with her schoolwork, they cook together, and he tells her stories about All Might. As time passes, Eri becomes more confident and starts to think about how she can use her quirk to help others, just like Izuku does. She might even start to train to become a hero herself one day.
The other characters at U.A. would likely be very supportive. Ochaco might become like an older sister to Eri, always there to cheer her up. Bakugo could be a tough - love type, teaching her to be strong. The teachers, like Aizawa, would keep an eye on her progress. They would also be a source of protection. The overall atmosphere at U.A. would become more family - like, with Eri as the new addition.
One possible plot could be that Izuku discovers Rei's hidden strength. Maybe Rei has some untapped quirk potential that Izuku, with his analytical mind, helps her realize. They could team up to face a new threat in the My Hero Academia world that requires both of their unique skills and experiences.
In the fanfiction, perhaps Stain trains Izuku because he believes Izuku has the purity of heart to use power in a way that Stain deems correct. Stain could teach Izuku how to analyze opponents better, which would enhance Izuku's ability to strategize in battles. Izuku might then start to question the current hero ranking system during his training. He could grow to be a hero who is more focused on the essence of heroism rather than just fame and recognition, which would make him stand out among his peers and also cause some friction with the more traditional heroes and hero agencies.
Healing is another major theme. Fanfics often explore how Eri heals from her traumas with the help of the kind - hearted characters in My Hero Academia. This can involve her mental and emotional healing as well as learning to live a normal life.
One plot idea could be Eri and Kouta teaming up to help other children in need. Since Eri has her unique quirk and Kouta has his own abilities, they could use them to bring comfort and protection to kids who are in difficult situations. For example, they might find a group of children who are being bullied by villains with weaker quirks and use their combined powers to fend them off.
One interesting 'eri my hero academia fanfiction' could be about Eri learning to control her quirk in new and unexpected ways. For example, she might start to use it not just for healing but also for defensive purposes, like creating shields made of her horn fragments. Another could be a story where Eri forms a special bond with one of the other students at UA, perhaps someone like Deku, and they train together to help her gain more confidence in her abilities.
Izuku could develop his own unique fighting style. He combines his knowledge of hero strategies and his physical abilities. Maybe he invents gadgets like Batman, which give him an edge in battles against quirk - users. This would make him stand out as a badass hero in the fanfiction world.
The plot might revolve around a strange phenomenon that links their two universes. Female Izuku and Giorno are brought together and at first are confused. However, they soon start to communicate and find that they are both heroes in their own right. They have to figure out how to get back to their respective worlds while also dealing with the feelings that start to develop between them. This could involve them learning from each other's combat and heroics techniques.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of 'eri my hero academia fanfiction' with different ratings and themes. Another option is FanFiction.net, which also has a decent number of stories related to Eri in the My Hero Academia universe. Just be sure to check the reviews and ratings of the stories to find the good ones.
One plot idea could be that Izuku and Momo are paired up for a special training mission. They have to learn to combine their quirks in new and unexpected ways. For example, Izuku's super strength could be used to enhance Momo's creation of large and complex structures. Another idea is a story where they both get trapped in an alternate dimension and have to rely on each other to find a way back. They face various challenges that test not only their quirks but also their friendship and trust in each other.