Yes, there might be such fanfics in the fandom. Some fanfic writers like to explore different interpretations of characters, and making Eren secretly a girl can bring a whole new perspective to the story. It could involve changes in relationships, plotlines, and character dynamics within the context of the original work's universe.
One possible plot twist could be how his relationships change. For example, his friends might react with shock and confusion at first. Mikasa might have a whole new set of emotions to deal with, like a different kind of protectiveness. Also, the military might view him differently. They could be hesitant to send a 'female - Eren' into battle at first, or they might use his new form to their advantage in different ways, like using his appearance to deceive the Titans.
One possible plot idea could be that Eren has been hiding her gender to fit into the military or a male - dominated society. As the story progresses, her secret could be gradually revealed, causing shockwaves among her comrades. This could lead to some characters having to re - evaluate their relationships with her, and there could be both positive and negative reactions.
Well, his character development could take a whole new turn. Eren is known for his aggression and determination as a male. As a girl, he might have to find new ways to express those traits. He could become more empathetic as he experiences different forms of discrimination or treatment. Also, his relationships with his male friends could become more complex. They might see him in a new light, and he might have to re - evaluate his own self - worth in relation to how they now view him. His development could also be influenced by how he copes with his new physical form and the limitations or advantages it might bring in the fight against Titans.
First, you need to establish the reason for the transformation. It could be a magical spell gone wrong, or some kind of strange dragon - related phenomenon. Then, focus on how Hiccup adjusts to her new body. She'll have to deal with different physical abilities and limitations. For example, she might be physically not as strong as before, but more agile in some ways.
A fanfic could explore how Hiccup's transformation into a girl affects his friendships. Astrid might react in a complex way. At first, she could be jealous or confused, but then they could form a stronger bond. Also, Hiccup's father, Stoick, might have a hard time adjusting to his son becoming a daughter, which could add a lot of emotional depth to the story.
One possible scenario in this fanfic could be that Tony Stark, through some sort of magic or scientific experiment gone wrong, turns into a girl. This could lead to a whole new set of adventures and character developments. For example, his relationships with other characters like Steve Rogers (Stony) would be completely different. He might have to face new challenges in a different physical form, such as how society and his friends would accept him. Also, his own self - perception would change, and he'd have to re - evaluate his identity.
Well, in a 'freed turns into a girl' fanfic, the plot might start with an experiment gone wrong. Freed was perhaps trying to enhance his magic power and something in the experiment caused his physical form to change to that of a girl. He would have to deal with the reactions of his guildmates. Some might tease him, while others would be more understanding. And he would also face challenges like how to adapt to the new body's physical limitations while still being able to participate in guild activities.
The fanfic might also explore how Issei's powers are affected by the transformation. In the original Highschool DxD, Issei has his own set of abilities as a male. But as a girl, he could either have new powers related to femininity in that universe or his existing powers could be modified. This could lead to new battles and challenges where he has to learn to use his powers in a different way.
Well, one possible plot could be that Deku accidentally drinks a strange potion created by a villain. This potion has the side - effect of changing his gender to female. At first, he's shocked and confused. But then, he realizes that he can use this new form to his advantage in hero work. For example, he might be able to infiltrate a female - only villain group more easily. He also has to deal with his friends' reactions, some are surprised while others are supportive and help him adjust to his new body while still being a hero.