One plot idea could be that Ken Kaneki somehow gets transported to the world of 'Fairy Tail'. He might initially be seen as a threat due to his ghoul nature, but as the story progresses, he could form alliances with the Fairy Tail guild members. Maybe he helps them fight against a common enemy that has some similarities to the ghoul - like threats in his own world.
Sure. You can try searching on popular fanfiction platforms like Archive of Our Own (AO3). There are likely many works that cross over Ken Kaneki from 'Tokyo Ghoul' with the world of 'Fairy Tail'. Just type in the relevant keywords in the search bar and you'll be presented with a variety of stories.
A crossover with "The Avengers" would also be cool. Kaneki could team up with the Avengers to fight against a common enemy that threatens both the human and ghoul worlds. His unique abilities would add an interesting element to the superhero team.
One idea could be a crossover with the world of 'Fullmetal Alchemist'. Kaneki Ken could be a chimera created by some dark alchemical experiment. His kagune could be seen as a strange alchemical creation. Another could be a crossover with 'Attack on Titan', where Kaneki joins the Survey Corps and uses his kagune to fight Titans in a unique way.
You can try fanfiction websites like Archive of Our Own (AO3). It has a large collection of fan - made stories, and there's a good chance you'll find 'fairy tail kaneki ken fanfiction' there.
One great 'fairy tail kaneki ken fanfiction' could be the one where Kaneki is transported to the Fairy Tail world and has to learn their magic. It's an interesting take on combining the two universes.
One idea could be a crossover with the 'Harry Potter' universe. Ken Kaneki could be a new student at Hogwarts, dealing with his ghoul powers while also learning magic. Another could be a crossover with 'Attack on Titan', where he helps the Scouts fight Titans, using his unique abilities. Or perhaps a crossover with 'My Hero Academia', where he attends UA and has to navigate the world of heroes and villains.
One idea could be a story where Naruto characters are transported to the Fairy Tail world. For example, Naruto himself could end up in Magnolia and join the Fairy Tail guild. He might use his ninja skills in combination with magic, creating unique combat styles. His Rasengan could be enhanced with magical elements, leading to new and powerful attacks.
One idea could be that the characters from Fairy Tail and Magi team up to defeat a common, extremely powerful dark magic user. The mages from Fairy Tail could use their unique magic skills like Natsu's fire magic, while the Magi characters could utilize their dungeon - conquering abilities and djinn powers. For example, Alibaba could use Amon's power in combination with Gray's ice - make magic to create some really cool and powerful attacks.
One idea could be that Sakura somehow gets transported to the Fairy Tail world. She could use her medical ninjutsu skills to heal the wizards in Fairy Tail, which would be a new and useful ability in that world. Maybe she teams up with Lucy and they go on adventures together, with Sakura providing combat support and healing when needed.
One idea could be Natsu crossing over into a modern-day world. He'd be confused by all the technology but use his magic in unexpected ways, like using fire magic to power up electrical devices. Another could be a crossover with a different anime world where Natsu has to team up with new characters to fight a common enemy. For example, in a world full of mecha, he might use his fire to overheat the enemy mechas.