Perhaps the story could be about Spike turning into a girl and using this new form to her advantage. She could infiltrate an all - girl group or event that was previously off - limits to her as a male dragon. In this new form, she discovers things about herself that she never knew before, like a love for singing or dancing. Along the way, she also has to deal with the fact that she may or may not want to stay in this form permanently and what that would mean for her identity and her relationships.
A possible plot could be centered around Spike's loyalty to Twilight. He discovers a secret that Twilight doesn't want anyone to know. Instead of thanking Spike for keeping it, Twilight blames him for finding out in the first place. This betrayal from Twilight, the one he admires the most, shatters Spike's world. He then has to decide whether to stay loyal or move on.
One possibility could be a story where Spike sacrifices himself to save his friends. Maybe there's a great danger in Equestria, like a powerful dark magic that only Spike can stop because of his unique dragon abilities. He might use his fire to counter the dark magic but in the process, exhausts all his energy and dies. His friends are left to mourn his loss but also remember him as a hero.
One possible plot could be that Pikachu, after being exposed to a strange form of energy in the Pokémon world, transforms into a girl. She then has to deal with the confusion of her new form while still having her Pikachu memories. She might struggle to fit into the Pokémon society in this new body, but also discovers new abilities or a deeper connection to certain types of Pokémon that she didn't have before.
In a fanfiction about Albedo turning into a girl, the story could begin with Albedo's research into some ancient alchemy. By accident, a reaction occurs that changes his gender. At first, he is horrified and tries to reverse it immediately. But as time passes, he starts to explore what it means to be a girl. He could make new friends among the female population in Mondstadt who help him understand the female perspective. His relationships with his old friends might also change. For example, some might become more protective, while others might be a bit distant at first, until they get used to the new Albedo.
Magic gone wrong is a common reason. Maybe a spell that Twilight was working on backfired and accidentally turned Spike into a pony.
One possible plot twist could be that Kakashi, as a girl, has to deal with different social expectations in the ninja world. For example, she might face more restrictions in combat training because of her new gender. Another could be that she uses her new form to her advantage in undercover missions, fooling enemies who are less likely to suspect a female. Also, there could be a romantic plot twist where a character who previously saw Kakashi as a rival now has different feelings for her as a girl.
Well, the plot could involve Sonic turning into a girl due to a magical curse. In this fanfiction, Sonic as a girl might struggle with the different social expectations in her world. For example, some characters might treat her differently just because she's female. However, she still retains her brave and adventurous spirit. She might team up with some female characters in the Sonic universe who help her understand and adapt to her new form. And of course, she'll still be out there fighting Dr. Eggman, but now with a new perspective and maybe some new combat moves that come with the female form.
One possible plot could be that Naruto, after being hit by a strange jutsu during a mission, turns into a little girl. His friends are initially shocked but then try to find a way to reverse it. Sakura might take on a big - sister role, protecting 'Naruko' from any potential threats while they search for a cure.
One possible plot could be that Sakura uses a new jutsu she's been working on accidentally and it turns Naruto into a girl. Naruto then has to deal with the sudden change, like how people in the village react differently to him/her. Maybe he/she has to learn new ways of fighting as a girl, with different physical abilities. And there could be some comical moments as Naruto tries to adapt to wearing girl's clothes and doing girl - like things.
Well, it could be a story where Canada turns into a girl due to some magical or mysterious event. As a girl, she discovers new aspects of her personality. She might become more assertive or more in touch with her emotions. And in terms of her relationships with the other Hetalia characters, she could form new friendships or rivalries. For instance, she might have a rivalry with France who is always a bit of a flirt and now sees her as a new target for his charm.