One idea could be a character using Polyjuice Potion to switch with a Death Eater to infiltrate their ranks and gather information for the Order of Phoenix. This would lead to a lot of tense moments as they try not to be discovered.
Hermione Granger is quite common. Since she's very intelligent and resourceful in the original series, in fanfiction she often uses the Polyjuice Potion for various purposes, like solving mysteries or getting access to restricted areas.
One idea could be a student using Polyjuice Potion to turn into a house - elf to spy on the Hogwarts kitchen secrets. They might discover a hidden passage that the house - elves use for their own purposes. Another could be turning into a hippogriff to experience flight in a new way and interact with other magical creatures from their perspective. Maybe a character uses it to turn into a Blast - Ended Skrewt to find out why they are so aggressive and what their purpose is in the wizarding world.
One interesting plot twist could be when the polyjuice potion is accidentally modified. For example, instead of just changing a person's appearance, it also gives them some of the magical abilities of the person they are transforming into. This could lead to a character who is normally not very powerful suddenly having extraordinary skills, which would completely change the power dynamics in the story.
One idea could be a situation where a group of Hogwarts students accidentally use the Polyjuice Potion and swap identities in the middle of an important exam. It would lead to chaos as they struggle to answer questions in each other's forms.
A possible plot is that Ginny accidentally drinks Polyjuice Potion that was meant for someone else. She transforms into an unknown person and gets lost in the wizarding world. Harry then has to find a way to reverse the effect and find her. He might have to go on a journey through different wizarding communities and face various challenges. Along the way, he discovers some secrets about the Polyjuice Potion that he didn't know before, like a rare ingredient that can make the potion's effect last much longer than normal.
One idea could be that a character accidentally drinks Polyjuice Potion made from a pregnant person and has to deal with the sudden physical changes and the reactions of others. They might have to keep up the pretense while trying to find a way to reverse the effects, all while exploring the magic behind the potion in a clean, exciting way.
Well, perhaps a character uses the potion to turn into a teacher to change grades in order to get a friend out of academic trouble. They end up having to teach a class while in the teacher's form and hilarity ensues as they struggle to keep up with the subject matter. It could also lead to some self - discovery for the character about the challenges of teaching.
Flur might use Polyjuice to change into a male character in a fanfiction. This could be a strategic move in a wizarding duel or a quest where being a male gives her certain advantages.
I'm not sure specifically which 'sexy polyjuice story' you're referring to. There could be many fictional stories involving polyjuice potion in the wizarding world. It might be a story where someone uses the polyjuice potion in a rather alluring or mysterious way, perhaps to transform into a desirable form.