Well, you could write a fanfiction where Voldemort is reborn not as a full - blown villain but as a conflicted character. He might start to question his past actions and try to make amends in a very strange way. Harry could be the one who has to guide him through this transformation, and there would be a lot of tension between the two. Also, what if Voldemort was actually an experiment gone wrong by some ancient wizards, and Harry discovers this truth and has to decide whether to expose it or keep it hidden for the sake of the wizarding world's stability. And then there's the idea of Voldemort's diary having a different kind of magic that instead of just influencing Ginny, it starts to influence Harry in a positive way, making him see Voldemort as a potential ally against a new, emerging dark force.
One idea could be that the child discovers a hidden portal in the house that leads to another fictional world. They then have to navigate this new world while also dealing with the secrets and mysteries of their own house. Another plot could involve the child having special powers that are awakened because of their connection to the house, and they use these powers to solve problems in both their world and the crossover world.
One idea could be a fanfiction where Voldemort has a change of heart due to some ancient magic. Maybe he discovers a spell that shows him the true consequences of his actions and decides to work with Harry to fix the wizarding world instead of destroying it.
One idea could be that Harry, influenced by dark magic, forms an uneasy alliance with Voldemort. They could team up to take over the wizarding world in a different way than Voldemort originally planned, perhaps by ruling jointly. Another plot could involve Harry exploring the darker aspects of his own magic and using some of Voldemort's knowledge to do so, which causes a rift between him and his friends.
One idea could be a fanfiction where Voldemort gets a second chance at life but without his dark magic powers. He has to learn to live as a normal wizard in the wizarding world and Harry Potter has to decide whether to trust him or not.
One idea could be a fanfiction where Voldemort is redeemed. Maybe after a near - death experience, he has a change of heart and tries to make amends for all the evil he has done. He could start by secretly helping Harry Potter against some other dark forces that emerge in the wizarding world.
Perhaps in this fanfiction, there could be a group of magical bats that are guardians of an ancient Hogwarts secret. Harry, as he befriends them in his bat form, gets drawn into this mystery. These bats could have their own language and culture that Harry has to learn. For example, they might communicate through a series of ultrasonic sounds that only a bat - like Harry - can understand. This could lead to a whole new adventure for Harry, separate from the main battles against Voldemort but still relevant to the overall protection of the wizarding world.
One unique plot idea is time - travel. For example, a character going back in time to change a crucial event in the wizarding world. Another is the idea of a Muggle - born wizard creating a new form of magic that combines Muggle technology and wizardry. And there are also stories where characters from different Hogwarts houses have to team up in unexpected ways to face a common threat.
A plot idea could be that a group of Hogwarts students accidentally travel to the Avatar world. They are then forced to learn bending in order to survive and find their way back home. Along the way, they discover that there are some similarities between magic and bending, like how both require focus and discipline.
One idea could be that Harry discovers a new spell that can penetrate Voldemort's dark magic defenses and uses it to shoot him. Another could be that Harry teams up with some unexpected allies, like the house - elves, who help him get in a position to shoot Voldemort. Maybe Harry has to sacrifice something important, like his invisibility cloak, to gain the power needed to fire the shot that will defeat Voldemort.
One interesting plot idea could be that Harry discovers a new and ancient magic that gives him an unexpected edge in the duel. For example, he might find a spell that can temporarily freeze Voldemort's dark magic, allowing Harry to strike. Another could be that Harry has a vision during the duel that shows him the true source of Voldemort's power, and he uses this knowledge to target it directly. Maybe it's a hidden object or a bond with a dark entity that Harry manages to sever, weakening Voldemort.