A fanfiction could explore what would happen if the magic from the Harry Potter universe was somehow combined with the powers of the Last Witch Hunter. For example, the Last Witch Hunter could gain the ability to use spells like Harry Potter, or Harry could get some of the unique skills of the Witch Hunter. This would lead to a whole new set of adventures and challenges for them both.
A plot could involve a group of witch hunters infiltrating Hogwarts. They think there are dark witches there, but they end up getting lost in the magical castle and start to see the beauty and positive aspects of magic. As they interact with students and teachers, they have to re - evaluate their views on witches and magic in general.
A fanfiction could focus on a character from Harry Potter who is a secret Hunter x Hunter fan. They could be constantly comparing the two worlds in their mind. Like how the Sorting Hat in Harry Potter is similar to the way Hunters are selected in Hunter x Hunter. Or how the Forbidden Forest in Harry Potter has some similarities to the Dark Continent in Hunter x Hunter.
One great 'Harry Potter and The Last Witch Hunter' fanfiction is 'The Crossover Chronicles'. It combines the magic of Harry Potter's world with the gritty, dark elements of The Last Witch Hunter. It has an interesting plot where Harry Potter teams up with the Witch Hunter to fight a new, powerful dark force that threatens both their worlds.
One of the most creative crossovers is the idea of a magical school in the world of The Last Witch Hunter, inspired by Hogwarts. In this fanfic, Witch Hunters' children start to attend this school, and they learn both traditional Witch Hunter skills and magic from the Harry Potter universe. It's a great mix of the two worlds' educational systems and magic concepts, and it shows how the two different cultures can blend together.
Perhaps a new type of creature that is neither from the Harry Potter world nor the Witch Hunter's world. It could be a result of some dark magic experiment gone wrong. This creature could have the ability to nullify magic in some ways, which would be a huge threat to both Harry and the Witch Hunter.
One idea could be a magical competition between Hogwarts and Cackle's Academy. Students from both schools could compete in various magical tasks, like a complex potion - making duel or a dangerous magical creature taming challenge. This would bring together the worlds of Harry Potter and The Worst Witch in a really exciting way.
Well, you could write a fanfiction where the Sorting Hat in Harry Potter is actually an ancient airbending relic. In the story, it could have the power to sense not just a student's Hogwarts house potential, but also their potential as a bender in the Last Airbender world. Also, imagine a plot where Dumbledore was once an acquaintance of an old Avatar and learned some airbending wisdom from him, which he then uses to guide Harry in his fight against evil. And a third idea might be a fanfic in which the Marauders were secretly training in bending arts during their Hogwarts days.
One idea could be that Harry Potter discovers a hidden world within the wizarding realm where Vampire Hunter D's technology and lore exist. He teams up with D to fight a new breed of vampires that are immune to normal wizarding spells. This would blend the magic of Harry Potter with the dark, post - apocalyptic feel of Vampire Hunter D.
Perhaps a group of wizards and witches form an alliance with Monster Hunters to stop a powerful dark magic - infused monster that is terrorizing both the wizarding world and the Monster Hunter's territory. They have to exchange knowledge, like the wizards teaching the Monster Hunters about potions for healing and the Monster Hunters showing the wizards how to use their unique weapons more effectively.
Perhaps Aunt Petunia is a witch who was cursed long ago. The curse made her forget her magic and act like a Muggle. When Harry unknowingly breaks the curse, she suddenly has her powers back. She then has to face the wizarding world again and deal with all the changes that have occurred since she last remembered her true self. She might even have some unique powers that are different from the norm because of the curse.