Maybe the plot could involve Kuroko having a secret crush on a boy in her group, but she can't show her true feelings because she's been hiding her gender. As the story unfolds, she has to deal with the internal struggle of wanting to be honest about who she is while also not wanting to disrupt the dynamic of the group she's in.
Another idea for the plot could be that Kuroko is in a world where girls are not allowed to participate in a certain activity, so she pretends to be a boy. However, as she gets closer to her friends in this activity, she realizes she can't keep the secret forever. There could be a lot of drama and tension as she tries to figure out when and how to reveal her true self.
The antagonists in the story, if there are any, could use Kuroko's secret against her. They might spread rumors or try to get her kicked out of the group she's in. On the other hand, some of the neutral characters could be swayed either way depending on how Kuroko presents herself and how the situation is handled.
In a 'kuroko turns into a girl fanfic', perhaps there's a magical event that causes the transformation. Kuroko, as a girl, could discover new aspects of his/her personality. For example, he/she might find that he/she is more in touch with emotions or has a different sense of style. And there could be a whole story about how he/she tries to fit into this new body while still maintaining his/her old relationships and goals.
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.
Well, perhaps the plot could involve Bilbo hiding her true gender identity in a world where being a girl might bring unexpected challenges or opportunities. Maybe she has to keep it a secret to be able to go on adventures like the male hobbits do. She could be constantly worried about being discovered while also having to deal with her own self - discovery and acceptance of her femininity.
In a 'lelouch is secretly a girl' fanfic, the plot could involve Lelouch's struggle with her identity. She may have been raised as a boy for strategic reasons. As she grows older, she starts to question her own identity. Meanwhile, her actions in the political and military arenas are constantly under scrutiny. When her secret is on the verge of being exposed, she has to make difficult decisions about who she really is and what she stands for. This could lead to a re - evaluation of all her relationships and her place in the world she has been fighting in.
The plot could involve Levi's past. Maybe she was forced to hide her gender to survive in a harsh environment. In the fanfic, she could gradually form a close bond with a particular character who starts to suspect something is different about her. This could lead to a conflict between her desire to keep the secret and her growing feelings for this character.
In the 'izuku secretly dating a girl fanfic', the plot could be that the girl is actually from a rival school. Izuku is initially hesitant about the relationship because of the potential conflict of interest. But their feelings for each other are too strong. They date secretly, and there could be some close calls where they almost get caught by classmates or teachers from either school.
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.
His friends from his original life could be main characters. For example, if he has a best friend, that person would play an important role in helping Kuroko adjust to being a girl. Maybe they would offer support and advice, or just be there to listen when Kuroko has a tough time dealing with the changes.
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.