Maybe a powerful Sith Lord discovers the magic of the Harry Potter world and decides to collect powerful witches and wizards to add to his 'harem' of followers. He could see their magic as a new source of power. This would lead to a conflict as the heroes from both universes try to stop him and rescue those who have been captured.
Well, a really interesting plot could involve a magical accident that transports some Star Wars characters to Hogwarts. They then have to adapt to the new environment and rules. At the same time, the Hogwarts students are fascinated by these strange new visitors with their lightsabers and different powers. There could also be a plot where a prophecy in the wizarding world is related to a Sith Lord from Star Wars, and both sides have to figure out how to deal with it together. This would involve a lot of character interaction, discovery of new cultures and powers, and the building of relationships between characters from the two very different universes.
One idea could be a wizard from the Harry Potter world accidentally getting transported to the Star Wars galaxy. They might use their magic in unexpected ways, like using a levitation charm to move starships. Another could be having Darth Vader encounter Voldemort. Vader's dark side power and Voldemort's dark magic would create a really intense showdown.
A cool plot would be a combined Hogwarts and Jedi academy. Younglings and first - year students could learn from each other. The Force and magic could be compared and contrasted. There could be a conflict when some students from each side start to envy the other's powers. And a big battle against a common enemy, like an ancient Sith - wizard hybrid, could bring them all together in the end.
One idea could be that the Jedi use magic like in Harry Potter. For example, they could use spells to enhance their lightsaber skills. Another plot could involve Harry Potter characters traveling to the Star Wars universe and learning to use the Force. Or perhaps Darth Vader could end up at Hogwarts and try to take over the school using the dark side of the Force and dark magic combined.
One idea could be that the Death Eaters team up with the Sith Lords. They could share their knowledge of dark magic and the Force, creating a super - powerful and evil alliance. The Jedi could then come to Hogwarts to help the Order of the Phoenix fight against this new threat.
One idea could be a young Jedi who falls to the dark side and starts to gather a harem of Sith apprentices, each with their own unique skills and backstories. They could all be on a quest to find an ancient Sith artifact that is said to grant ultimate power.
One idea could be focusing on a young clone trooper who discovers he has unique Force abilities. He then has to hide this from his superiors while trying to figure out what it means.
One idea could be exploring the backstories of the clone troopers in more detail. Maybe focus on a particular clone and his relationships with his brothers. Another could be creating a new adventure for Anakin Skywalker during the Clone Wars that wasn't shown in the original series. For example, he could be sent on a secret mission to a planet that has a powerful and ancient Sith artifact.
One interesting concept could be the merging of magical elements from Harry Potter and the space - faring aspects of Star Wars. For example, a character might use a magic spell while flying a starship. Another concept could be the interaction between different species from both universes in the context of a harem. The unique cultures in Harry Potter like the wizarding houses and those in Star Wars such as the Jedi and Sith could also create complex relationship dynamics in the harem fanfiction.
One idea could be that in a magical multiverse crossover, Harry Potter and Spider - Man end up in a world where a harem of characters from both universes exist. Maybe Harry uses his magic to help Spider - Man fight villains in this new world, and they both start to form relationships with the female characters in the harem.