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.
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.
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.
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.
In a fanfiction with Naruto and Nana Shimura, Naruto's character can be developed in terms of leadership. He could learn from Nana Shimura how to lead in a more diplomatic way. Nana Shimura's character development could come from her adapting to the modern ninja world that Naruto represents. She might have to change some of her old - fashioned views. Also, their relationship could develop Naruto's patience. Nana Shimura might be more reserved or strict, and Naruto would need to be patient with her, which would be a new aspect of his character growth.
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.