Maybe in the fanfiction, Natsu turns into a girl due to a magical experiment gone wrong. His guild mates react in various ways. Some are amused, while others are worried. As a girl, Natsu has to navigate the world in a different body. He might start to notice how differently people treat him compared to when he was a boy. He could then use this new perspective to his advantage in future battles or quests, all while trying to reverse the transformation.
One possible plot could be that Natsu, after being hit by a strange magic spell during a battle, turns into a girl. His friends are initially shocked but quickly adapt. Natsu, as a girl, discovers new aspects of his own personality. For example, he might find that he is more in touch with his emotions. He could also face some challenges like having to deal with different clothing styles and the way others now perceive him. As the story progresses, he tries to find a way to break the spell while still learning important lessons about himself and his relationships with others.
Well, in the fanfiction, it could start with Natsu waking up as a girl one day with no memory of how it happened. He would be confused and a bit scared at first. His closest friends like Lucy would help him get used to his new form. Natsu would find that he has different physical abilities now as a girl. He may be more agile or have different magical energy flow. And throughout the story, he would be on a journey to find out who or what caused this transformation and how to turn back to his original self.
Maybe in the fanfiction, Natsu's emotional state causes him to turn into a dragon. After a great loss or a fit of extreme rage, his magic reacts and he transforms. This new form is both a blessing and a curse. It gives him the power to protect his loved ones better but also isolates him as he struggles to understand and control his new dragon instincts.
One possible plot could be that the magic in the world goes haywire. Natsu is caught in a spell that turns him into a baby. His friends in Fairy Tail are shocked at first. Lucy might take on the role of a caretaker, trying to figure out how to reverse the spell while also dealing with a baby Natsu's unpredictable behavior like randomly using small bursts of fire magic that are more like cute little puffs now.
Well, one possible plot could be that Goku, as a girl, has to face different challenges in the martial arts world. Maybe the other fighters underestimate her at first, but she quickly proves them wrong with her incredible strength and skills. She might also have to deal with new emotions and how others perceive her femininity in the context of being a powerful fighter.
Well, perhaps the story could revolve around Kirito's relationships. As a girl, his/her interactions with Asuna could change significantly. They might develop a different kind of friendship or even a romantic relationship that has new dynamics compared to when Kirito was male. Also, other characters like Klein might react in very interesting ways to this transformation.
One possible plot could be that Merlin, after being hit by a strange spell, turns into a girl. His friends in Camelot are initially shocked. Arthur might be both confused and a bit protective in a new way. Merlin has to deal with the new physical form while still trying to protect Arthur and Camelot. She would have to adapt to the different expectations placed on women in Camelot, like different dress codes and social behaviors, all while hiding her true identity as the powerful sorcerer Merlin.
One possible plot could be that Sonic, after being exposed to a strange Chaos Emerald malfunction, turns into a girl. As a girl, Sonic might face new challenges in terms of her identity. For example, her friends like Tails and Knuckles might initially be confused. Sonic could then have to deal with different reactions from her enemies too. Maybe Dr. Eggman would underestimate her in this new form, but she would prove him wrong by using her speed and skills in new and unexpected ways. She might also discover new aspects of her own personality that were hidden before the transformation.
The plot could involve a mad scientist who was experimenting with a new type of candy - to - human transformation. The gumball was an accidental subject. Once it turns into a girl, she discovers that she has some unique abilities related to her gumball origin. For example, she can bounce really high or is super sweet - smelling. She then uses these abilities to help her new friends in the town she finds herself in, and at the same time, tries to reverse the transformation if she wants to.
One possible plot could be that Firestar, as a girl, has to face different challenges in the clan. Maybe she is initially not accepted by some cats who are used to the male Firestar. But she proves herself by her hunting and fighting skills. She might also have a different perspective on relationships within the clan, like forming new friendships with female cats and having a different dynamic with male cats.
Perhaps in this fanfiction, when Natsu becomes an adult, he decides to explore different parts of the magical world that he was previously unable to reach. He could discover new types of magic or encounter different magical creatures. This could lead to him bringing back new knowledge to his guild, and they could use it to strengthen themselves. Also, his transformation might make him more of a leader figure within the guild, guiding the younger members.
Well, perhaps in this fanfiction, Aang turns into a girl due to some strange magic or spirit encounter. And then she finds that she can connect with certain female spirits in a new way. This leads her on a journey to understand this new aspect of herself and also use this new connection to bring balance to the world in ways she hadn't considered before.