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.
It could explore the themes of identity. In Harry Potter, characters struggle with their wizard identity and their place in the magical world. Tokyo Ghoul characters deal with their half - human, half - ghoul nature. And in High School DxD, the devils have their own hierarchy and sense of self. A fanfic could bring these themes together by having characters from different universes question who they really are when faced with the cultures and powers of the other two universes. For example, a ghoul might be inspired by the acceptance of different species in the Harry Potter world and try to find a new way to exist without having to constantly hide or hunt.
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.
First, you need to understand the core elements of each series. For Harry Potter, it's the magic system, the houses at Hogwarts, and the battle between good and evil. In Tokyo Ghoul, it's the ghoul society, the kagune powers, and the struggle for survival. And for High School DxD, it's the devil's hierarchy, the Sacred Gears, and the harem aspect. Then, create a unique plot that can incorporate these elements. For example, you could start with a portal opening between the three worlds and characters getting sucked into different universes.
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 possible plot could be a crossover where the magic from Harry Potter world somehow seeps into the High School DxD universe. For example, the Hogwarts students end up in the DxD world and have to adapt to the different rules regarding devils, angels and fallen angels. They could use their magic to help or hinder the various factions in DxD depending on their motives.
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.
There's a fanfiction titled 'Hybrid Realms'. In this one, the author creates a whole new scenario where the two universes are on the verge of merging. The main characters from both Tokyo Ghoul and High School DxD have to team up to prevent chaos. It has a great plot with lots of action and character development.
Well, in a Tokyo Ghoul and Harry Potter crossover fanfiction, there could be a character who is both a ghoul and a wizard. This character would have to struggle with the dual nature of their existence. On one hand, they have the magic of the wizarding world, but on the other, they have the hunger for human flesh as a ghoul. They might use magic to try and control their ghoul instincts, like using a spell to suppress the urge to attack people.
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.
The popularity of such fanfiction lies in the unique combination of two very different worlds. Tokyo Ghoul has its dark, gritty atmosphere with ghouls and their struggle for survival. High School DxD, on the other hand, has a more flamboyant and supernatural high - school - like setting. When combined, it creates a new and exciting narrative space.