In this fanfiction, a new teacher arrives at Hogwarts who has a passion for both magic and glee. This teacher decides to start a glee - like club at Hogwarts. Harry and his friends are intrigued and join. They discover that music has a special power in the wizarding world. It can be used to unlock hidden magical abilities. The club then prepares for a big magical glee competition against other magical schools, with each performance having a unique magical twist.
Well, perhaps Byako is a being from another dimension. In the 'Harry Potter meets Byako fanfiction', Byako could accidentally cross over into the Harry Potter universe while being chased by some sort of other - dimensional foe. Harry and his friends could help Byako hide from this enemy while also learning about different forms of magic from Byako's world.
A plot could involve Sherlock being a wizard all along but not realizing it until he meets Harry Potter. He has been using his logical mind to do what he thought was normal detective work, but it was actually his latent magic powers at play. Together, they could solve crimes in both the Muggle and wizarding worlds, using Sherlock's methods and Harry's knowledge of magic spells and potions.
Perhaps in the fanfiction, the Ministry of Magic mistakes Loki for a powerful dark wizard. They try to capture him, but Loki easily evades their attempts. Harry Potter, being curious, decides to find out who this strange wizard is on his own. When they meet, Loki is initially hostile, but as they start to talk, they realize they both have a lot in common in terms of fighting against powerful and often misunderstood forces. They then form an uneasy alliance to face a new threat that is emerging in both their worlds.
Maybe Voldemort has some sort of connection to a powerful criminal in Spiderman's world. Harry and Spiderman team up to stop Voldemort from getting his hands on some high - tech weaponry from Spiderman's universe. Spiderman teaches Harry some of his combat moves, and Harry shows Spiderman some basic spells.
One possible plot could be that Harry Potter, during one of his adventures in the Forbidden Forest, stumbles upon a magical portal that transports him to the world where Byakko exists. Byakko, being a powerful and mysterious creature, initially sees Harry as a threat. But as Harry shows his kind heart and magical abilities, they form an unlikely alliance. They could team up to fight a common enemy, perhaps a dark wizard who has also found his way into Byakko's world and is causing chaos there.
One possible plot could be that the magical creatures in the Harry Potter world start to show up in Forks. For example, a hippogriff might fly over the forest near Bella's house, causing chaos among the vampires and werewolves. The wizards from Hogwarts could come to investigate these strange new creatures that seem to have a different kind of magic than what they're used to. Harry, Hermione, and Ron could find themselves in the middle of the vampire - werewolf feud, trying to figure out how to keep the peace and also protect the muggles in Forks from getting too involved in this new magical mess.
Maybe in the fanfiction, Harry accidentally enters a parallel dimension where Lily is still alive. Here, Lily discovers that Harry is her future son. She might take him under her wing and train him in a different way of magic, one that was perhaps forgotten in Harry's own time. This could lead to Harry having unique powers and a different approach to dealing with the Dark Arts and his enemies.
One interesting crossover could be the characters from Glee performing at Hogwarts. Imagine the Glee club singing in the Great Hall, bringing their modern music to the magical world. It would be a great mix of the two universes.
Perhaps a crossover where the Glee characters get sorted into Hogwarts houses. Santana could be a Slytherin, Finn a Gryffindor. And then there could be stories about how they adapt to the magical school environment, with their singing talents adding a new dimension to the Hogwarts experience.
One idea could be that Harry Potter and his friends accidentally get transported to the RWBY world. They could then use their magic in unique ways to help the RWBY characters fight Grimm. For example, Hermione could use her knowledge of spells to create new defenses against the Grimm that the RWBY characters haven't thought of before.