One possible plot could be that England, as a girl, might start exploring her new identity in a modern world. She could face challenges in adapting to the social norms for women while still carrying the historical and cultural essence of England within her.
Even fictional characters from English literature could be involved. Sherlock Holmes could be brought into the story to help solve any mysteries that might arise due to England's transformation. He could use his deductive skills to figure out the cause and consequences of this strange event.
Her personality might not change drastically at first. England is known for being reserved and proud. As a girl, she could still be those things, but perhaps be more in touch with her emotions. For example, she might be more likely to show when she's hurt or offended instead of bottling it up like she might have as a male.
One possible scenario could be that in this fanfiction, the change forces Kratos to view the world from a different perspective. As a girl, he might face different challenges and reactions from the other characters. Maybe the gods who once feared him now underestimate him, leading to some interesting power dynamics.
Perhaps in a parallel universe, Superman is born as a girl. This version of her grows up with different experiences and challenges. She could be more in tune with female issues in society and use her powers to fight for gender equality as well as the usual superhero stuff like saving the world from villains and disasters.
Another possibility is that Finn - now a girl - discovers new powers or abilities that were hidden before. Since in many stories, a change in gender can sometimes bring out different aspects of a character. She could use these newfound powers to fight against the villains in Ooo in a more creative way than before.
Maybe in this fanfiction, Midoriya as a girl discovers new aspects of her power. Since her body has changed, the way she channels her quirk might also be different. She could then have to train all over again to master this new way of using her ability.
Physically, of course, there would be obvious changes. But personality - wise, he might become more in touch with his emotions. In the original, Lelouch was often very calculating and hid his true feelings. As a girl, society in the story might expect her to be more open about her emotions, which could force her to confront and express them more.
One idea could be that Steven turns into a girl due to a magical mishap. Maybe he was trying to help a gem with a spell and it backfired. As a girl, he could struggle with how others perceive him differently, but also discover new aspects of his personality. He might have to learn new ways to fight and use his powers, adding an interesting twist to the story.
A possible fanfiction plot could involve Sherlock's friends' reactions to his transformation. Watson might be initially shocked but then adapt and see that Sherlock is still the same brilliant mind, just in a different form. Mycroft could be more concerned about how this transformation affects Sherlock's standing in the intelligence community. And Lestrade might be confused but still rely on Sherlock's skills to solve difficult cases, albeit with some awkward moments at first due to the change.