One idea could be a crossover where a character from Harry Potter accidentally travels to the world of Tokyo Ghoul and Seikirei. They might use their magic to help in the battles against the ghouls in Tokyo Ghoul and get involved with the spirit battles in Seikirei. For example, Harry Potter himself could arrive and use spells like 'Stupefy' to stun the ghouls or use magic to protect the Sekirei from harm.
One idea could be a crossover where a character from Harry Potter accidentally enters the world of Tokyo Ghoul. Medusa could be incorporated as a dark force or an ancient evil that has somehow influenced both worlds. Maybe she has the power to turn ghouls into stone, which throws the already complex ecosystem of Tokyo Ghoul into chaos. And in the Harry Potter side, her presence could be related to dark magic spells that are long forgotten.
One idea could be a crossover where a vampire from the Harry Potter universe somehow ends up in the world of Tokyo Ghoul. Maybe a vampire who was hiding in the Forbidden Forest gets transported to Tokyo and has to adapt to the new rules of the Tokyo Ghoul world, dealing with ghouls and the CCG. This could lead to some interesting power dynamics as the vampire's magic might be a new factor in the Tokyo Ghoul ecosystem.
A great plot twist could be that the Horcruxes from Harry Potter are actually related to the source of the ghouls' power in Tokyo Ghoul. Maybe Voldemort had some connection to the origin of the ghouls long ago. Another twist could be that the Sekirei are actually the result of a failed magical experiment in the Harry Potter world that got transported to their own universe. So when the Harry Potter characters find out, they have to figure out how to reverse the experiment or control the Sekirei better.
Another concept is a crossover of the powers. In the fanfic, Weiss could have some sort of ice - based kagune, which combines her Schnee family glyph powers with the unique abilities of a Tokyo Ghoul. Blake could use her shadow powers in a way that is similar to how ghouls move in the shadows, making her a more stealthy fighter in the Tokyo Ghoul setting.
It could be really interesting. Maybe the wizards in Harry Potter world have to face the ghouls from Tokyo Ghoul. The magic spells could be used to fight against the kagune of the ghouls. For example, the Stunning Spell might stun a ghoul temporarily, giving the wizard a chance to escape or attack further.
It could be a wild and unique story. Imagine the magic of Harry Potter in the same world as the ghouls from Tokyo Ghoul and the devilish elements of High School DxD. Maybe the characters from each would form unexpected alliances. For example, a Hogwarts student could team up with a ghoul to fight against the devils from High School DxD in a battle for some sort of magical artifact. Or perhaps the different power systems would interact in strange ways, like a wizard using spells to counter a ghoul's kagune while also fending off a devil's power attack.
There are indeed. In some 'Harry Potter Tokyo Ghoul fanfic', the authors might explore how the magic in Harry Potter could be used to either cure or control the 'ghoul' condition in Tokyo Ghoul. It could also involve crossovers of characters, like Harry Potter and Kaneki Ken meeting and having to work together to solve a problem that affects both their worlds. This kind of fanfic often attracts fans of both series who are eager to see new and unexpected combinations.
A great Tokyo Ghoul - Harry Potter fanfic might involve a crossover of the two universes' magic systems. Imagine if the spells in Harry Potter could be used to control or counteract the ghouls' powers. Some fics could explore how the ghouls' need for human flesh might be affected by the presence of magic potions that could substitute it. You can often find these types of fics on fanfic websites like Archive of Our Own or Fanfiction.net by simply searching for 'Tokyo Ghoul Harry Potter crossover'.
One idea could be a story where a Wendigo somehow enters the wizarding world of Harry Potter. Maybe it's brought in by a dark wizard who wants to use it as a weapon. The Trio - Harry, Ron, and Hermione - would then have to figure out how to defeat it using their magic and knowledge.
One idea could be that Hulk somehow gets transported into the wizarding world of Harry Potter. Maybe a magical experiment gone wrong by a Hogwarts student creates a portal that sucks Hulk in. He could then cause chaos as he's not used to the magic and strange creatures there.