There could also be new characters introduced in the fanfiction. Maybe a female wizard who befriends Harry in his new form and helps him understand the female side of the wizarding world better. Or perhaps a villain who specifically targets Harry because of his unique transformation, seeing it as a weakness to be exploited.
One interesting plot could be that as a girl, Harry has to navigate the different social dynamics in Hogwarts. For example, he might be treated differently by his male friends who now see him as a girl. They could be more protective or act a bit awkward around him.
One possible plot could be that Naruto turns into a girl to infiltrate an all - female organization that is suspected of having ties to a new threat. As a girl, he has to deal with the different social dynamics among the women, like cattiness in some cases but also strong sisterly bonds. He also has to hide his true identity while trying to gather information.
Well, perhaps a plotline could involve Sasuke turning into a girl and using this new form to his advantage in some undercover mission. He could infiltrate an enemy group more easily as a girl. Also, there could be a love triangle where some of the characters who previously saw Sasuke as a male now have different feelings towards him as a girl, which would create a lot of drama and conflict.
Sakura might be initially shocked and a bit jealous at how cute Naruto - as - a - girl is. Sasuke would probably be confused at first but then act indifferent. Kakashi would be his usual calm self, but might crack a few jokes about Naruto's new look.
In addition to the obvious ones like Naruto and Sakura, other characters from Sasuke's clan might interact with him. For instance, if there are any remaining Uchiha members, they might have mixed reactions. Some could be shocked and try to figure out what happened, while others might be more accepting. Also, characters like Shikamaru, who is very observant, would surely notice the change in Sasuke and might have some unique interactions, perhaps trying to figure out how this change could affect their team dynamics or the overall situation in the village.
Perhaps the plot could involve Petunia having some sort of magical awakening or discovery that leads her to perform this transformation on Harry. In this fanfiction, Harry might then use her new female identity to infiltrate parts of the wizarding world that are more difficult for a male to access, like certain all - female magical groups. And this could lead to all sorts of adventures and revelations about the wizarding world's gender dynamics.
Another possibility is that it's an accidental result of a powerful magic clash between Voldemort and Harry. When their magic collides in a certain way, it causes an unexpected transformation on Harry, turning him into a girl. This would add a whole new layer of complexity to their relationship and the overall story.
Petunia's character could also develop in this fanfiction. If she turns Harry into a girl, she might start to feel guilty or responsible. This could lead to a change in her relationship with Harry. Maybe she would start to see Harry as more of a person rather than just a burden. And she could also develop some magical abilities further as she has now performed such a complex spell on Harry.
A great plotline could be that Harry, now a girl, has to navigate the world of wizarding fashion and etiquette which she previously ignored. She might be forced to attend more social events at Hogwarts, like balls or tea parties, where she has to learn proper behavior. And she could also use her new identity to her advantage when it comes to spying on the Death Eaters. They might underestimate her because she's a girl, but she could outwit them.