A plot could involve Ginny being the key to defeating Voldemort once and for all in a way that no one expected. Since she has a strong connection to Harry, and Harry was once a Horcrux of Voldemort, perhaps her magic has a unique ability to target and destroy the remaining essence of Voldemort. This could lead to a thrilling adventure where Harry and Ginny have to work together in a very different way than before to finally rid the wizarding world of Voldemort's threat.
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.
Perhaps a plot where Voldemort discovers that Lucius has been having doubts about his leadership. He then tasks Snape with spying on Lucius. Meanwhile, Harry, through some magical accident, gets involved in this web of intrigue. The story could be about how Harry uses this situation to his advantage to try and bring down Voldemort's regime from within.
Well, a plot could be that Voldemort has a change of heart after falling in love with Ginny. He starts to question his dark ways and Ginny, seeing this potential for good in him, decides to marry him in the hopes of fully turning him around. But this is met with great resistance from the wizarding community who see Voldemort as irredeemable. Ginny then has to fight not only for Voldemort's redemption but also for their relationship to be accepted.
A possible plot is that there's a mysterious illness spreading among the Quidditch players, and Harry and Ginny have to figure out what's causing it and how to stop it before the big Quidditch tournament. Or perhaps a new and dangerous Quidditch move is introduced by a visiting team, and Harry and Ginny must learn it quickly to stay competitive. They could also have a friendly rivalry with another couple who are also big Quidditch fans.
Perhaps there's a magical guitar that Harry and Ginny find. It has special powers, like when Ginny plays it, it can calm the most ferocious magical creatures. They go on a journey to figure out the origin of the guitar and along the way, their relationship deepens as they face various challenges together.
One idea could be that Harry and Ginny are swimming in a secret pool at Hogwarts that has some magical properties. Maybe the pool can change its shape or temperature based on their emotions. Another could be that they are having a swimming race to train for a Triwizard Tournament - like event for adults. And they use magic to enhance their swimming abilities in creative ways.
One idea could be that Harry starts having strange dreams where he sees through Voldemort's eyes. This could lead to him unknowingly helping Voldemort in some small ways at first, like revealing the location of some minor Order of the Phoenix safe houses. Another plot could involve the other characters slowly realizing something is wrong with Harry. For example, Hermione might notice that Harry is using some Dark Magic spells without hesitation, which is completely out of character for him.
A plot could involve a magical creature that bonds Harry and Voldemort in an unexpected way. For example, a rare faerie that makes them see each other's memories. Through this, Harry discovers some long - hidden secrets about Voldemort's past that could potentially change the course of their enmity. They then have to decide what to do with this new - found knowledge.
One plot idea could be that Harry gives himself to Voldemort in an attempt to understand the Dark Lord's mind and find a weakness from within. Another could be that he sacrifices himself this way to protect his friends and Hogwarts, believing that there's a way to turn Voldemort's victory into a defeat from the inside. Or perhaps Harry has a vision that shows this as the only way to truly end the war and he decides to take the risk.
One plot idea could be that they discover they are mates due to a powerful magical bond. They then have to hide this fact from the wizarding world which is in the midst of a war. Harry might try to convince Voldemort to abandon his dark ways, using their newfound connection as a way to appeal to his better nature.