One example could be a story where the magic system from Harry Potter is merged with the technological and crystal - based powers in Final Fantasy XIII. For instance, characters from the Harry Potter world might use wands to access the power of the crystals in Final Fantasy XIII. Another could be a crossover where the characters have to travel between the two universes, like Harry and his friends ending up in the world of Final Fantasy XIII and having to adapt to its rules and help the locals fight against a common enemy, perhaps an evil force that threatens both worlds.
Some fanfictions might focus on a character from Final Fantasy XIII, say Lightning, ending up at Hogwarts. She could be mistaken for a new kind of magical being and have to learn about the wizarding world while also using her own combat skills. Or it could be about a Harry Potter character, like Hermione, studying the technology and lore of Final Fantasy XIII in order to find a solution to a problem in the wizarding world, like a new kind of dark magic that can only be countered with knowledge from the other universe.
There could be a fanfiction where the Hogwarts houses are combined with the l'Cie and Cie'th concepts from Final Fantasy XIII. For example, students in Gryffindor could be more likely to become l'Cie with a certain set of powers related to courage, while Slytherin students might be tempted by the dark side of the l'Cie power. This would create an interesting dynamic where the two different sets of concepts interact and influence each other in new and unexpected ways.
One example could be a story where the characters from Harry Potter find themselves in the world of Final Fantasy 8. Maybe Harry uses his magic in the same way Squall uses his gunblade, creating unique battle scenarios. Another could be a crossover where the spells in Harry Potter are combined with the junction system of Final Fantasy 8, leading to some really interesting power - ups for the characters.
The worlds can be blended through character crossovers. For example, Vaan from Final Fantasy XIII could visit Hogwarts and be amazed by the magic there. He could try to learn magic spells, while also teaching the wizards about his world's combat skills.
One great fanfiction could be about a wizard from the Harry Potter world being transported to the world of Final Fantasy 13. Maybe they have to learn the new magic system there while also trying to find a way back home. It could be full of exciting battles and new friendships.
One interesting fanfiction could be a crossover where the magic from Harry Potter meets the high - tech world of Final Fantasy 7. For example, imagine Harry and his friends being transported to Midgar and having to deal with Shinra while also using their magic. There are likely some out there that explore how the different magic systems interact, like how materia could be related to wand magic. Another aspect could be the characters' reactions to the different cultures. Harry might be shocked by the slums in Midgar, while Cloud and his group could be intrigued by Hogwarts and its secrets.
One idea could be a crossover where Sephiroth somehow ends up in the wizarding world of Harry Potter. Maybe he's a dark force that Voldemort tries to use for his own gain, but Sephiroth has his own agenda. He could use his powerful magic, which is different from the magic in the Potterverse, to create chaos.
One example could be a story where the magic from Harry Potter is introduced into the Star Wars universe. Maybe the Jedi could learn spells like the wizards in Hogwarts. Another could be a crossover where Harry Potter characters find themselves in the Star Wars galaxy and have to adapt to the use of the Force instead of magic. For instance, Harry could be mistaken for a young Jedi in training.
One interesting 'Final Fantasy XIII Fanfiction' story could be about the characters' lives after the main events of the game. For example, a story where Lightning is trying to rebuild society in a more peaceful way. Another could be a fanfiction that focuses on the relationship between Snow and Serah, exploring their love story in more depth. There are also those that might give backstories to the minor characters, making them more fleshed out and interesting.
There could be a crossover where some of the characters from Harry Potter end up in the Assassination Classroom. Harry, Hermione, and Ron might find themselves in the classroom, and they'd bring their own set of skills and knowledge. Hermione would probably be very interested in Koro - sensei's unique biology and try to figure out how to use magic to defeat him based on that knowledge.
One great example could be a story where a wizard from the Harry Potter world discovers ancient Valyrian magic spells. This could lead to all sorts of interesting plot twists, like using the powerful Valyrian magic to combat dark wizards in the Harry Potter universe. Another could be a crossover where a character from the Valyrian era is transported to Hogwarts and has to adapt to the different magical system there.
There could be fanfictions where characters from Harry Potter end up in the World of Warcraft universe and encounter Sylviana - like perhaps Hermione using her magic knowledge to solve some of the Warcraft's mysteries while teaming up with Sylviana. However, it's quite a niche combination, so finding existing examples might be a bit challenging. One could start by looking in specialized fanfiction archives and forums dedicated to crossover stories.