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 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 through the mind link, Harry discovers Voldemort's hidden fears from his past, like his fear of being abandoned as an orphan. This could give Harry an edge in their final battles.
One plot idea could be that the female Voldemort has a change of heart. Maybe she starts to see the error of Voldemort's ways after interacting with Harry Potter. She could start to secretly help Harry and his friends against the Death Eaters, which would create a lot of internal conflict within the Dark side.
One way to make Voldemort more complex is to give him a moral code, albeit a twisted one. He might believe that his actions of purging the wizarding world of Muggle - borns are for the greater good of the pure - blood wizards. This would make him more than just a one - dimensional villain. Also, explore his relationship with magic itself. He's extremely powerful, but what if there are certain types of magic that he respects or fears? Maybe there are ancient magics that he believes could either destroy him or make him truly invincible. And don't forget to explore his mental state. He's clearly not a normal, well - adjusted wizard. Maybe he has hallucinations or voices in his head that he has to deal with, which could be a result of his dark magic use or his fractured soul. This would make him a much more complex and interesting character in your fanfiction.