Well, perhaps a plot could involve Ed as a girl having to deal with the different expectations society has for her. For example, in combat situations, opponents might underestimate her because she's a girl. And she could use this to her advantage in some cases. Also, her relationships with her brother Alphonse might change in some ways as she is now a girl secretly. Maybe there are new emotional dynamics between them.
One idea could be that Ed has to keep her true gender a secret while on her alchemic adventures to avoid discrimination in a male - dominated alchemic world. Another could be that she forms unique relationships with other characters who might suspect or eventually discover her secret.
One idea could be that as a girl secretly, Ed Elric might face different challenges in the male - dominated alchemist world. Maybe she has to hide her true identity while trying to achieve her alchemical goals.
The plot could also involve Ed using her new - found female identity to her advantage in some situations. For example, in a world where people might underestimate a girl in alchemy, she could surprise them with her skills. Or she could use her femininity to gain access to certain places or information that were previously unavailable to her as a boy. This could create all sorts of interesting twists and turns in the story as she navigates the world of alchemy with this secret identity.
One possible plotline could be that Ed has been hiding her true gender to fit into a male - dominated society or group. Maybe she's afraid of being discriminated against. Another could be that she falls in love with someone who initially only sees her as a male friend, and then there's the big reveal.
Alphonse could be a major supporting character. Since he is Ed's brother, he would be in a unique position to either help her keep the secret or accidentally almost expose it. Winry could also be important. She might be someone Ed could confide in or struggle to keep the secret from, especially if their relationship takes on new dimensions due to Ed's secret gender.
In this type of fanfiction, a great plot idea could be that Naruto's female identity is tied to some sort of ancient prophecy. Only as a girl can she fulfill this prophecy which could involve saving the ninja world in a different way than in the original story. Her secrecy then becomes crucial not just for her own safety but for the fate of the entire world. And as she tries to keep her secret, she has to navigate the challenges of being a girl in a world that expects her to be a boy.
In this fanfiction, her role as an alchemist might be perceived differently. As a girl, she might face more discrimination in the male - dominated field of alchemy. This could lead to stories of her having to prove herself more often and in different ways than in the original story.
A possible plot for the 'Tsuna is secretly a girl' fanfiction could be that Tsuna is a talented athlete in a boys - only sports team. She has to keep her gender a secret because she's afraid of losing her position. However, as she gets closer to her teammates, she realizes that they would accept her for who she is. Along the way, there could be a rival from another team who discovers her secret and tries to use it against her, but in the end, Tsuna overcomes this obstacle and is able to be open about being a girl.
One idea could be that Percy, as a girl, has to deal with different expectations in the demigod world. For example, some might assume she's not as strong physically, but she proves them wrong by outperforming many male demigods in combat training. Another plot could involve her having a different kind of relationship with Annabeth. Instead of the typical male - female friendship - romance dynamic, they could have a more sisterly bond that still has elements of competitiveness and deep mutual respect.
One plot idea could be that Sasuke has been secretly a girl all along but has been hiding it to fit into the male - dominated ninja world. She could struggle with her identity while also having to deal with her feelings for Naruto in a new light. Another idea is that she's a girl in disguise to seek revenge on those who wronged her family, and as the story progresses, her true self starts to emerge.
Perhaps in the fanfiction, Izuku as a girl might have a different relationship dynamic with her friends. Her friendships with male characters could take on a new aspect, like a protective or sisterly role. It could also add a new layer to her relationship with Bakugo, maybe changing the nature of their rivalry to something more complex due to gender differences.