One idea could be a story where a young Death Eater in training is forced to use the Cruciatus Curse on an innocent by his family, but he has a change of heart. He then has to deal with the consequences of defying his family's wishes and trying to protect the victim from further harm.
Perhaps a fanfic could center around a group of Hogwarts students who discover a dark artifact that enhances the power of the Cruciatus Curse. They must race against time to destroy it before it falls into the wrong hands. They face many challenges and moral dilemmas along the way. For example, some might be tempted to use the enhanced curse against their enemies, but they know it's wrong. This creates internal conflicts within the group.
In a fanfiction, the plot could revolve around Bellatrix misusing the Cruciatus Curse and getting in trouble with Voldemort. She uses it on one of Voldemort's favored servants by mistake. Voldemort then has to decide whether to punish Bellatrix severely or let her off with a warning, while Bellatrix tries to plead her case and shift the blame onto others.
Well, you could have a fanfic where Harry himself is forced to fight the Imperius Curse in a new and unexpected way. Maybe he has to use his connection with Voldemort to resist it when Voldemort tries to use it on him during a crucial battle. Or perhaps a story about how Hermione discovers a new counter - curse to the Imperius Curse by researching in the restricted section of the library.
One idea could be a situation where a misbehaving Hogwarts student accidentally casts a modified spanking curse on themselves during a spell - misfiring experiment. Another could be a dark wizard using the spanking curse in a new and devious way to torment his enemies, but the heroes have to figure out how to counter it using their knowledge of magic. Maybe there could also be a comical take where the curse is used as a form of punishment in a very light - hearted way among friends, like when they play a magical prank too far.
Show the physical and mental toll it takes on the victim. For example, describe how the victim's body contorts painfully and their mind is filled with unbearable agony. Maybe the victim has nightmares about the curse long after it has been used on them.
One idea could be a story where a young curse breaker discovers a long - forgotten and extremely powerful curse in the Forbidden Forest. They then have to race against time to find a way to break it before it starts to affect the entire Hogwarts. Another could be about a curse breaker who is wrongly accused of creating new curses and has to prove their innocence while also breaking real curses that are plaguing the wizarding world. Maybe a curse breaker could be sent on a mission to an ancient wizarding ruin, filled with curses, to retrieve a powerful magical artifact.
A fanfiction might explore the backstory of Bellatrix's use of the Cruciatus Curse. Perhaps she was first introduced to it as a young witch at Hogwarts by some dark wizarding group. She practiced it on small animals, which led to her getting in trouble. But this early experience with the curse made her more interested in the Dark Arts, and she continued to perfect her use of Crucio as she grew older and became a Death Eater.
A possible plot in Harry Potter curse mark fanfiction is that the curse mark is actually a key to an ancient wizarding mystery. The main character, who has the mark, finds that they are suddenly being hunted by dark forces who want to use the mark for their own evil purposes. As the character tries to figure out what the mark means and how to protect themselves, they discover that it is linked to a prophecy. They must then decide whether to embrace the power that the mark might bring or find a way to destroy it completely, all while dealing with the normal challenges of Hogwarts life like exams and friendships.
One idea could be a new, unknown curse that has no known cure in the original series, and the fanfiction focuses on a young witch or wizard inventing a unique cure through trial and error. Maybe they use a combination of rare magical plants and spells.
An idea could be that there is an ice cream that can show memories when you eat it. In the fanfic, Harry Potter could eat this ice cream and relive some of his forgotten or suppressed memories about his parents. This would add an emotional depth to the story and also be a unique use of the ice - cream concept within the 'Harry Potter' world.
One idea could be a crossover where Harry and Neville end up in the Naruto universe. They could learn chakra techniques and use their magic in new ways. For example, Harry might combine his Patronus charm with a chakra-based attack. Neville could use his knowledge of Herbology to discover new medicinal plants in the Naruto world.