Perhaps the characters from Fast and Furious accidentally stumble into the wizarding world. They then get involved in a race against time, literally, as they help Harry Potter and his friends stop a time - related dark spell. The cars could be enchanted to fly or perform other magical feats.
One idea could be that the wizards in the Harry Potter world need to learn some fast - paced driving skills from the Fast and Furious crew to escape a new dark magic threat that is spreading quickly. They could use magic to enhance the cars' capabilities.
One interesting plot idea is having the characters from Fast and Furious enter the Triwizard Tournament in the Harry Potter world. Imagine Dom Toretto competing in a magical challenge on a broomstick. Another is Harry Potter characters using magic to help the Fast and Furious gang in a high - stakes car chase against some dark magic - using villains.
One way to combine them could be to have the characters from Fast and Furious enter the wizarding world of Harry Potter. For example, Dominic Toretto could drive his car into Hogwarts, causing a stir among the students and teachers. Maybe his car has some sort of magical ability that gets noticed by the wizards.
A fanfiction could also explore how the rest of the crew in the Fast and Furious family reacts to Mia's pregnancy. Do they become over - protective? Or do they try to keep things as normal as possible while still being excited for the new baby?
One idea could be that Elena discovers she's pregnant during a time of relative calm in the Fast and Furious world. She then has to decide whether to tell Dom or keep it a secret for a while. Maybe she's worried about how it will affect his dangerous lifestyle.
One idea could be a crossover where Harry Potter accidentally travels to the One Piece world and meets Whitebeard. He could learn about their different forms of magic and power, and together they face a new threat that combines the dark magic from his world and the powerful pirates in the One Piece world.
One idea could be a crossover where Harry Potter accidentally ends up in the world of Ranma 1/2. Maybe he's on a magical experiment gone wrong and lands in Nerima. He could use his magic to help Ranma deal with his curse, like creating a spell to keep him from changing into a girl when splashed with cold water.
Another concept could be a crossover where the magic in the Harry Potter universe has an unexpected effect on Android 18. For example, it could start to interact with her android systems in strange ways, giving her new powers or abilities that are a combination of magic and her android technology. This would lead to a whole new set of adventures as she tries to figure out what's happening to her.
One idea could be that Gandalf somehow gets transported to the Harry Potter universe. He could become a mentor to Harry, using his vast magical knowledge and wisdom from Middle - earth. Maybe he helps Harry understand some ancient magic that even Dumbledore wasn't fully aware of.
One idea could be that Hawkgirl somehow gets transported to the Harry Potter universe. Maybe she arrives during a Quidditch match and her flying skills astound everyone. She could then join forces with Harry and his friends to fight against the dark forces in Hogwarts, using her Nth metal mace and flight abilities in unique ways.
One interesting plot is if there is a magical race in the wizarding world that is inspired by the races in Fast and Furious. The cars in this race could be enchanted and the drivers could use both magic and driving skills. Hermione could use her intelligence to come up with new strategies for the race, while Dom could show off his amazing driving stunts.