One idea could be that the Hogwarts students are transported to the world of RWBY. They could learn about Dust and how it's different from magic. For example, Harry could befriend Ruby and they could exchange knowledge about their respective powers. Harry might teach Ruby some basic spells while Ruby shows Harry how to use Crescent Rose.
A fun concept could be a magical school in the RWBY universe. The students could be taught both magic from the Harry Potter world and combat skills from RWBY. Characters like Hermione would thrive in this environment, using her knowledge of magic to enhance the combat training. And Weiss could learn new spells to incorporate into her Dust - based attacks.
Well, perhaps the female Harry Potter is transported to the RWBY world due to a magical accident. In this new world, she realizes that the concept of magic is different but still has some similarities. She could start a school of magic in the RWBY world, teaching students both magic spells and the values she learned at Hogwarts. Her presence might also attract the attention of some of the more shadowy organizations in RWBY, who see her magic as a powerful tool to be either controlled or destroyed.
One interesting idea could be a crossover of different timelines within RWBY. For example, characters from the past meet the current ones and have to deal with the differences in their worlds. Another could be a crossover of different teams in unexpected ways, like Team RWBY having to team up with a rival team to face a common enemy that is more powerful than any they've faced before. And sometimes, there are crossovers that involve alternate versions of the characters, where their personalities or abilities are slightly different, which can lead to very unique and engaging storylines.
A really cool plot could be that Voldemort somehow follows Harry into the RWBY world. This would force the RWBY characters and Harry to team up against this new and powerful threat. Harry would have to teach the RWBY crew about the nature of Voldemort and his Horcruxes, while the RWBY team would introduce Harry to the ways of fighting Grimm and using Dust. It would be a clash of two very different magical systems and a great opportunity for character development and epic battles.
A crossover could involve a magical pet from Harry Potter being transferred to the RWBY world. For example, a phoenix. The RWBY characters would be amazed by this magical creature. The phoenix could help them in battles against Grimm. It could also have a connection with one of the RWBY characters, like giving them the ability to rise from the ashes, literally or metaphorically, after a tough battle.
Another possibility is that Voldemort somehow discovers the world of Narnia and tries to conquer it. This would force the Narnian characters to team up with the Order of the Phoenix. Harry Potter and his friends could learn about the talking animals and different forms of magic in Narnia, while the Narnian heroes would see the power of wizardry. It could lead to a great adventure full of battles and new friendships.
A cool Harry Potter OC Crossover Fanfiction idea could be to have an OC crossover with the world of Middle - earth. Imagine an OC from Hogwarts traveling to Middle - earth and using their magic to help in the battles against Sauron. They could introduce wands and spells to the hobbits and elves. Also, a crossover with the world of Fairy Tail would be interesting. The OC could join the Fairy Tail guild and participate in their quests while also showing off the unique magic of the Harry Potter universe. And a crossover with the world of Howl's Moving Castle could be fun too. The OC could interact with Howl and Sophie and learn about their form of magic which is different from Hogwarts magic.
One idea could be a magical exchange program. Wizards from Hogwarts and Dragon Riders from Alagaësia meet and learn from each other's magical systems. Harry Potter characters could be fascinated by the bond between Eragon and his dragon Saphira, while Eragon might be intrigued by the variety of magic at Hogwarts like Transfiguration and Potions.
One idea could be having Harry Potter characters attend an anime - style magic school in Japan. For example, Harry could be a transfer student to a school where they teach magic in a very different way compared to Hogwarts, with elements like anime - inspired uniforms and more focus on martial arts - based magic.
Perhaps there could be a magical object in 'Harry Potter' that is somehow related to the werewolves in 'The Howling'. For example, a spell book that has the secrets to controlling werewolf transformations. The characters from both worlds could be on a quest to find this book and in the process, they learn more about each other's worlds and how magic works differently in each.
A great idea for 'harry potter and friends crossover fanfiction' is a crossover with 'Narnia'. The magical world of Narnia and Hogwarts have some similarities. Harry and his friends could enter Narnia through a magical portal in Hogwarts. They could help the Pevensie children in their battles against the White Witch. Another option is a crossover with 'The Chronicles of Prydain'. Harry and his friends could journey to Prydain and encounter the magical creatures and challenges there. And a crossover with 'Fantastic Beasts' but in a different way, like the main characters from 'Harry Potter' meet Newt's ancestors and have adventures with them.