Well, it could be that a rift in the multiverse brings the two universes together. The Avengers are confused by the presence of ghouls, and the ghouls are equally shocked by the high - tech world of the Avengers. Some of the Avengers might be disgusted by the ghouls' need to eat human flesh at first. However, through some events, like a big attack on both their worlds, they realize they need to collaborate. The Avengers could help the ghouls find an alternative food source, while the ghouls could use their combat skills to aid the Avengers in battle.
The plot could involve the ghouls from Tokyo Ghoul being brought into the Avengers' world. Maybe the Avengers initially mistake the ghouls for new, dangerous threats. But as they learn more about the ghouls' situation, they might try to find a way to co - exist. For example, Kaneki could share his story with the Avengers, and they could be sympathetic. Then they could team up to fight a common enemy, like a new type of super - villain who wants to use the power of ghouls for evil purposes.
The plot might focus on the struggle for identity that both Kaneki and Shinichi face. Kaneki is caught between his human and ghoul sides, while Shinichi has to deal with having a parasite in him. In the crossover fanfic, they could exchange their experiences and learn from each other. They might also encounter a new type of being that combines the traits of ghouls and parasites, which forces them to re - evaluate their own identities and how they fit into this new world of the crossover.
Definitely Thor and Tsukiyama. Thor, the god of thunder, with his powerful hammer, and Tsukiyama, the flamboyant ghoul. Tsukiyama's refined tastes and his kagune skills could be paired with Thor's brute strength. They could have some hilarious banter as they fight side by side against enemies. And also, Black Widow and Touka could be a great pair. Black Widow's spy skills and Touka's street - smart and combat - ready nature would make them a formidable duo.
One possible plot could be a character from Tokyo Ghoul ending up in the world of Vampire Knight. Maybe Kaneki, with his unique ghoul powers, could interact with the vampires and hunters in Vampire Knight. He might initially be seen as a threat, but as the story progresses, they could find common ground in their struggle for survival in a world that fears them.
Well, it could start with a strange portal opening up that transports some of the Tokyo Ghoul characters into the Devilman's world or vice versa. At first, there would be confusion and mistrust. But as they start to understand each other's situations, they realize that they need to work together. The story could then explore how their different powers interact. Like, how would the CCG's quinque weapons fare against Devilman's foes? And how would the Devilman's allies react to the existence of ghouls?
Well, it could be about Jedi or Sith characters finding themselves in the Tokyo Ghoul universe. Maybe a Jedi has to use the Force to deal with the ghouls' kagune. They might try to bring peace between humans and ghouls, like they do in their own galaxy with different species.
The plot could start with Batman getting an invitation from SHIELD. They've noticed some strange activities in Gotham that seem related to a threat that could affect the whole world. Batman joins the Avengers. He quickly realizes that their methods are very different from his. But he uses his stealth and detective skills to gather information that the Avengers couldn't. For example, he discovers a hidden base of the villains by following a small clue.
Hermione would probably be extremely curious about the ghouls. She'd want to study their biology, especially the kagune. She might even try to find a way to use her magic to help the half - human, half - ghoul characters like Kaneki deal with their identity crisis.
The storyline could be really interesting. Maybe the ghouls could be a new kind of dark creature in the Harry Potter world. The characters from Tokyo Ghoul, like Ken Kaneki, might attend Hogwarts. He could struggle with his ghoul nature while trying to fit in with the wizards and witches. The magic in the Harry Potter universe could also have an impact on the ghouls' abilities, perhaps suppressing or enhancing them.
One popular crossover idea could be with 'Attack on Titan'. Picture Tokyo Ghoul characters in the world of Titans, fighting alongside or against the Survey Corps. Another could be with 'Fullmetal Alchemist', where the alchemical concepts might interact with the ghoul powers. For example, an alchemist trying to find a way to cure the ghouls or control their kagune.
A crossover story could be really exciting. In this kind of fanfiction, we might see the Survey Corps from Attack on Titan having to deal with the ghouls from Tokyo Ghoul. Maybe Eren and his friends would be confused at first about these new, strange creatures that are part human, part something else. They could initially mistake the ghouls for Titans. And the ghouls, on the other hand, would be equally shocked by the Titans and the advanced technology the Attack on Titan characters use. It would be a clash of two very different but equally dark and violent worlds.