Well, perhaps there is a dark wizard who is using Muggle - born wizards and witches as pawns in a larger scheme. Some of these Muggle - borns are related to the Reagan family in Blue Bloods. The Hogwarts students and the Reagans then team up to rescue the Muggle - borns and stop the dark wizard. Harry Potter himself could be involved, mentoring the Muggle - borns in their new magical abilities while the Reagans use their knowledge of the Muggle world to track down the dark wizard's lair in the non - magical parts of the city.
One idea could be that the magical world of Harry Potter somehow intersects with the police - family - centered world of Blue Bloods. Maybe a wizard or witch commits a crime in the non - magical world, and the Reagan family from Blue Bloods has to deal with it while also trying to understand the magical elements involved. For example, a magical object is stolen and being used to cause chaos in New York City, and the Hogwarts students come to help solve the mystery, with the Reagans providing their non - magical expertise.
Hermione Granger and Erin Reagan could be an interesting duo. Hermione is brilliant and well - read in the magical arts, and Erin is a smart lawyer. They could work together on a case where a wizard is on trial in the non - magical world for using magic in a way that breaks Muggle laws. Hermione could provide the magical knowledge and Erin could handle the legal aspects in the non - magical court system.
Well, perhaps there's a cursed object in the evidence room of the Blue Bloods precinct. The Winchesters hear about it through their hunter network and come to investigate. Along the way, they start to bond with the Reagan family members. Danny Reagan could be initially skeptical of the Winchesters' methods but gradually come to respect their skills in dealing with the supernatural. They could all work together to break the curse on the object before it causes more harm.
A crossover fanfiction might have the law - enforcement aspects of both combined. For instance, the NYPD officers from Blue Bloods could learn from the unique ways that the Zootopia police deal with their diverse population of animals. Or perhaps an animal from Zootopia travels to the city in Blue Bloods and causes some chaos due to their different nature, and both sets of characters have to figure out how to handle it.
Well, perhaps the magical creatures from the Harry Potter universe end up in the '300' setting. Dragons could be used by the Spartans to fight their enemies. The centaurs could also join the battle, lending their archery skills. And Harry could learn some combat skills from the Spartans, which he could then use back in the wizarding world to fight Voldemort's Death Eaters.
The Stargate could be a portal between different magical realms in the Harry Potter universe. For example, it could lead to a place where ancient and more powerful magic exists. Wizards from different schools around the world could team up with Stargate explorers to uncover the secrets of this new place. There might be a new threat emerging from this realm that requires both magic and Stargate technology to defeat. This would bring together characters like Harry Potter and Jack O'Neill to lead the charge against the common enemy.
Well, perhaps there's a rift in the multiverse that connects Central City to Hogwarts. The Flash, while chasing a villain, gets sucked into the wizarding world. Harry Potter and his friends initially suspect him as a threat but then realize his good intentions. They then combine their powers - the Flash's speed and the magic of the wizards - to fight a common enemy. For example, the Flash could use his speed to distribute protective spells all over Hogwarts really quickly, while Harry and his friends focus on the offensive magic against the bad guys.
One idea could be that Carly and her friends discover a magical portal in their apartment that leads to Hogwarts. They then have to navigate the wizarding world, with Carly being fascinated by all the magic. Meanwhile, Harry Potter and his friends are intrigued by the strange Muggle - like devices the iCarly gang has. They end up teaming up to solve a mystery that involves both the wizarding and Muggle worlds.
Well, perhaps the Death Note from the Bleach universe gets mixed up with the magic in Harry Potter's world. A powerful wizard could get hold of it and start using it in ways that disrupt the balance of life and death in both worlds. Harry and his friends would have to figure out how to stop this misuse, with the help of some Bleach characters who understand the true nature of the Death Note.
One idea could be that Eragon, while on one of his adventures in Alagaësia, accidentally creates a portal that leads him to Hogwarts. There, he meets Harry Potter and they quickly realize they have a lot in common. They could team up to fight against a dark force that somehow threatens both their worlds, like a new type of dark magic that combines the magic of Alagaësia and the dark arts from the wizarding world.
In a more comical plot, Hagrid could accidentally stumble upon a small Transformer while in the Forbidden Forest. Thinking it's a strange magical creature, he brings it back to Hogwarts. The Transformer, being a bit lost in this new magical world, causes all sorts of chaos in the castle. Harry and his friends have to figure out how to get the Transformer back to where it belongs while also dealing with the daily challenges at Hogwarts.