In some fanfictions, Harry might die sacrificing himself to save the wizarding world. However, the magic that Voldemort used to kill him had an unforeseen side effect. It sent Harry's soul into a sort of limbo where time doesn't exist. There, he meets a mysterious entity that gives him a second chance at life. When he returns, he has a different perspective on magic and starts to reform the wizarding world's education system to better prepare young wizards for the future threats.
One interesting plot could be that after Harry's death, his friends find a powerful ancient spell in the Room of Requirement. This spell was created long ago by a powerful wizard who also faced death unfairly. They manage to perform the spell and it brings Harry back. But he returns with some new powers that he has to learn to control. He also has a connection to the spirit world now, which helps him in his new battles against the remaining dark forces.
A plot could be that Harry's death triggers a magical reaction in Hogwarts itself. The castle, which has a life of its own, uses its magic to bring Harry back. But he is not the same Harry. He comes back as a spectral form at first. With the help of his friends and the magic of Hogwarts, he gradually regains his physical form. Along the way, he discovers secrets about Hogwarts that were long forgotten and uses this knowledge to bring about a new era of peace in the wizarding world.
Another plot could involve the Hufflepuff's hard - working trait turning into something more sinister. The Hufflepuffs are working hard not for good grades or to help others, but to build a powerful dark force within the school. Harry, as a part of this dark Hufflepuff, slowly realizes what's going on and has to decide whether to join in or fight against it, all while being influenced by the dark undertones of the house.
One plot could be that in a dark version, Harry and Luna team up to expose a hidden, evil regime within the wizarding world that has been secretly controlling things from the shadows. They might have to use some rather unorthodox and darker magic to do so.
One plot could be that in a dark world, Harry Potter is influenced by dark magic and Tonks, with her Metamorphmagus abilities, tries to spy on him for the Order but gets caught in his web of newfound power. She has to then fight her own feelings as she was once his ally.
One possible plot could be that the female vampire is initially an enemy but then becomes an ally to Harry. Maybe she has some information about Voldemort's dark magic that is linked to her vampire lore. Another plot could be a love story where Harry has to overcome the fact that she's a vampire and deal with the wizarding world's reaction to their relationship.
One possible plot could be that female Harry Potter is wrongly accused and sent to Azkaban. There, she discovers a hidden conspiracy within the prison walls. Maybe she finds out that some dark wizards are using Azkaban as a base to plan an attack on Hogwarts. Another plot might involve her using her unique magic skills, different from the male Harry Potter's in some ways, to survive the Dementors and break free, all while uncovering the truth about her false imprisonment.
The plot where Murtagh teaches Harry some of his unique magic techniques is really cool. It shows how different magical systems can interact. For example, in a fanfic I read, Murtagh showed Harry how to use a spell that was common in his world but unheard of in Hogwarts.
One possible plot could be that in a darker version of the wizarding world, Harry and Daphne form an alliance to uncover a hidden conspiracy within Hogwarts. Maybe they suspect that some of the professors are involved in a dark magic experiment that endangers the students. They have to navigate through the secrets and lies, using their combined skills and knowledge. Harry's combat experience and Daphne's knowledge of pure - blood family secrets might be the key to solving the mystery.
In some WBWL fanfictions, Harry is ostracized by the wizarding world because they believe he's not the 'true' savior. This makes him turn dark. He might form an alliance with Voldemort's followers out of spite. The plots often explore how his personality changes. He could become more ruthless and calculating, using his natural magical talent in ways that are more self - serving rather than for the greater good.
One plot could be that Snape, under some dark magic influence, forces Harry to accompany him on a dangerous mission to retrieve a lost magical artifact. Snape believes Harry has some hidden power that can help. Another could be Snape forcing Harry to study a very advanced and dangerous form of magic, thinking it will protect Harry in the long run. And there could also be a plot where Snape forces Harry to enter a magically sealed area to face some long - forgotten threat that only Harry can potentially defeat.
Perhaps Davy Jones' locker has a connection to the Chamber of Secrets. In the fanfiction, Harry discovers this link and has to journey into Davy Jones' locker to find a way to defeat Voldemort. Along the way, he has to face the horrors of the locker, including Davy Jones himself and his crew of the Flying Dutchman. This could be a really dark and exciting adventure.