A possible plot could be that Harry Potter discovers a prophecy that involves Fleur and a powerful vampire. The prophecy states that only together can they defeat a new dark force rising. Along the way, Fleur has to struggle with her own identity as she is part Veela and now has vampire traits after an encounter, and Harry has to deal with the mistrust of the wizarding community towards Fleur's new state.
One idea could be that Tonks discovers a hidden vampire community in the wizarding world while on a mission related to Harry Potter. Maybe the vampires are being wrongly accused of attacking wizards, and Tonks, with Harry's help, tries to uncover the truth.
One interesting plot could be Fleur and Harry teaming up for a dangerous magical quest that was previously thought impossible. They could use their unique magical skills, like Fleur's Veela charm and Harry's Parseltongue ability, to overcome various obstacles.
A more complex plot could be that there are some dark forces at play during the Yule Ball, and Fleur and Harry have to work together to stop them. They use their combined magical abilities, Harry's knowledge of Hogwarts and Fleur's Beauxbatons training, to overcome the threat and in the process, their relationship deepens.
One idea could be that they grow up learning magic together in a unique way. Maybe they discover a new spell or form of magic that no one else has. Another plot could involve them facing a common enemy from a young age and having to rely on each other's unique skills. For example, Fleur's Veela charm and Harry's Gryffindor courage could combine to defeat the foe.
A possible plot could be that after the war, Harry is in need of a fresh start. Fleur, who has always been attracted to his heroic nature, offers him a chance at a new life in France. Their marriage is a journey of self - discovery for both of them. Harry learns about the different wizarding traditions in France, and Fleur gets to know the more reserved side of Harry better. They build a relationship based on mutual respect and the shared goal of creating a peaceful future for the wizarding world.
Perhaps in the fanfiction, Fleur could be in danger during one of the Triwizard Tournament tasks. Harry, being the heroic type, decides to risk everything to save her. This act of heroism not only changes their relationship but also how the other champions and the judges view Harry. It could also lead to some changes in the overall dynamic of the tournament, like new rules being implemented to prevent such dangerous situations in the future.
One idea could be a post - war fanfic where Fleur and Harry work together to rebuild the wizarding world. They could use their unique skills and experiences to help those affected by the war. For example, Fleur's knowledge of Beauxbatons and international magic could be combined with Harry's leadership skills to create new international magical alliances.
Fleur could use her Veela charm to try and disarm or distract vampires. Since Veela have a certain allure, it might work on vampires as well.
One idea could be that Harry and Fleur travel back to the time of the founders of Hogwarts. They could witness the creation of the houses and perhaps even influence some of the early magical traditions. For example, they might help Gryffindor and Slytherin better understand each other, which could have a huge impact on the future of Hogwarts and the wizarding world.
Perhaps in this fanfiction, they are both part of a secret magic study group at Hogwarts. They study ancient and powerful magics together, and as they grow closer, they discover a hidden prophecy that involves both of them and has to do with the future of the wizarding world. Their relationship develops as they try to figure out what the prophecy means.