Here's a plot twist: The nappy was placed on Hermione by a future version of herself. In the future, Hogwarts is in great danger, and she has found a way to send this nappy back in time to her current self. The nappy contains a message or a spell component that she needs to save Hogwarts in the future. So it's not just a random nappy but a crucial part of a time - bending plan to save the school.
One idea could be a humorous fanfiction where Hermione accidentally gets turned into a baby by a misfired spell at Hogwarts and has to deal with wearing a nappy while her friends try to reverse the spell. It could be full of comical situations like her trying to communicate her intelligence while in a baby's body.
One possible plot twist could be that the baby has some unexpected magical abilities right from birth. Maybe it can communicate with magical creatures in a way no one has seen before. This would add an interesting element to the story as everyone at Hogwarts tries to figure out what it means.
Rather than exploring the plot of this particular fanfiction, it's better to look for fanfiction that showcases Hermione's intelligence, bravery, and positive qualities. Fanfiction has the potential to expand on the good aspects of a character, not to degrade them in such a way.
It might be that Draco is part of a spell experiment in Hogwarts and something goes haywire, resulting in him being in a nappy and getting caught. This could be part of a humorous fanfiction where his pride takes a huge blow.
I don't think it's ethical. Hermione is a beloved character from the Harry Potter series. Fanfiction should be a way to explore different aspects of a character's personality in a positive or at least non - harmful way. Blackmail is a negative and often immoral concept. Placing Hermione in such a situation in a nappy (which may imply a state of vulnerability or infantilization) seems more like a form of exploitation of the character rather than a legitimate creative exploration.
Perhaps in the fanfiction, Hogwarts decides to send a group of students to study the Muggle world up close with the Dursleys as their hosts. But what if the Dursleys are secretly working for a dark wizard who wants to use this opportunity to infiltrate Hogwarts? That would be a huge plot twist.
One possible plot twist could be that Draco actually has noble intentions behind the kidnapping. Maybe he's trying to protect Hermione from a greater threat that she's unaware of. For example, there could be a dark wizard targeting her specifically, and Draco, despite his past enmity, decides to take matters into his own hands to keep her safe.
Maybe she discovers a hidden prophecy that states she has the power to either destroy Voldemort or become his most powerful ally. This would create a great internal struggle for her as she was raised by him but also has a sense of good. She might start to manipulate Voldemort into making decisions that would eventually lead to his downfall.
One possible plot twist could be that Hermione discovers a hidden power within herself that is not in the original books. For example, she might find out she has a special connection to an ancient magic that only warriors possess. This could change her role in the wizarding world completely and lead her on a new adventure to master this power.
One possible plot could be that in a darker, alternate version of Hogwarts, there is a mysterious 'collar stripper' who targets Hermione. Maybe it's a new form of dark magic or a person under the influence of some evil force. Hermione, being the intelligent and brave witch she is, tries to figure out the mystery behind this 'collar stripper' and how it relates to the safety of Hogwarts and her friends.