Well, perhaps the plot could revolve around Percy hiding her true identity as a girl in a world where she's expected to be male. Maybe she's in a situation like a boarding school or a fantasy adventure setting, and she has to constantly keep up the facade while also dealing with her own self - discovery and the challenges that come with it.
Well, it could be that Gray has been hiding her true female identity all along. Maybe she's in a world where being a girl is not accepted in a certain context, like in a male - dominated sport or a strict military - like organization. And the fanfiction could revolve around her struggles to keep her secret while also trying to fit in and pursue her dreams.
Well, it could be that Stiles is secretly a girl and in the fanfiction, this secret is slowly revealed as he falls in love with someone. And the person he loves starts to notice little things that don't quite add up with his supposed male identity, like his more delicate features or his different style of communication.
Well, one possible plot twist could be that Natsu has been hiding her true gender to be able to participate in male - dominated activities like a certain guild or sport. Another could be that she's in love with a male character, but is afraid to reveal her gender in case it changes how he feels. Or perhaps she has a special power that is related to her being a girl secretly, like a unique form of magic that only female dragonslayers can possess.
Perhaps in this fanfiction, Bilbo is secretly a girl who has a great love for adventure but is restricted by the gender norms of her world. She disguises herself as a boy to join the dwarves on their journey. Along the way, she could fall in love with one of the characters, and her secret might be in danger of being exposed when they start to have more intimate moments. Her internal struggle between her true self and the false identity she has created could be a central part of the story.
One possible plot twist could be that Zoro's gender is revealed at a crucial moment, causing shock among the other characters. For example, during a battle when an enemy discovers this secret and uses it to try and throw the team off balance.
One possible plot could be that Percy gradually discovers his godly nature throughout the story. At first, he notices strange things happening around him, like being able to control certain elements without knowing why. As he investigates, he uncovers the truth about his divinity and has to deal with the fact that he's been living a lie.
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.
Another possible main character could be a rival. A person who is always competing with Percy and who might use the discovery of her secret as a weapon against her. This would add a lot of conflict to the story.
Maybe Ichigo is secretly a girl because she's on a secret mission. In the fanfiction, she could be a spy or an undercover agent. Her guise as a boy has allowed her to infiltrate certain groups or places. When her true identity as a girl is discovered, it throws the whole mission into chaos, and she has to find a way to salvage it while dealing with the personal relationships that are affected.
The plot could involve Gaara trying to hide her gender while still being a powerful shinobi. Maybe she has to constantly worry about being discovered during battles or in interactions with other ninja. For instance, she might have to come up with excuses for not sharing certain spaces with male ninja.