Well, 'Nana Shimura: Unseen Tales' is worth checking out. It's a fanfic that fills in the gaps in her story. It has detailed descriptions of her daily life and her struggles. The author does a great job of making her seem like a real, relatable person rather than just a character from a story.
You can start by looking on fanfiction websites like Archive of Our Own. They usually have a wide range of fanfictions, including ones about Nana Shimura.
Another aspect could be a story where Nana Shimura somehow survives and has to face the new world of heroes. How would she react to the current state of hero society? She might be shocked by the commercialization of heroism and try to bring back the purer form of being a hero that she knew.
One possible plot could be that Izuku, in his journey to become a great hero, discovers some hidden knowledge or power left behind by Nana Shimura. He might find an old diary or a secret training ground that was once used by her. This encounter could give him new insights and inspiration for his hero training.
A common theme is her relationship with her students or proteges. Since she was an important figure in the 'Boku no Hero' world, many fanfics explore how she influenced the younger heroes.
Some popular themes could be adventure. Since Naruto is known for his adventurous spirit, it could be combined with Nana Shimura's characteristics in a story where they embark on a journey together, perhaps to save the ninja world from a new threat. Another theme might be redemption. If the fanfiction explores Nana Shimura's past actions, Naruto could be the one to help her find redemption in the eyes of the ninja community. Also, friendship is a common theme. Their different backgrounds and abilities could make for an interesting friendship dynamic in the story.
When writing a nana shimura fanfic, it's important to stay true to her essence. She is a complex character with a strong sense of justice. Build on that. You can introduce new conflicts that test her beliefs. Also, pay attention to the setting. Whether it's the same world as the original or a new, alternate universe, make it feel real. Write detailed descriptions of the places and how Nana interacts with them. And don't be afraid to get feedback from other fans. They can give you great ideas and point out areas for improvement.
A simple fanfiction could be about a young hero in training who discovers Nana Shimura's old diary. Through reading it, they learn about her values and ideals, and are inspired to become a better hero themselves.