One idea could be creating an OC who is a powerful mage from a hidden village. They could join the main characters on their journey and use their unique magic to help in battles. For example, magic that can manipulate time briefly to give an advantage in combat.
Another interesting concept is an OC that is a mechanic. This OC could be in charge of upgrading the Regalia, the car in FF15. They could have a backstory of learning their skills from an old master in a far - off land and bring a whole new level of customization to the vehicle.
One idea could be exploring the backstory of an original character (OC) within the world of FF7. For example, an OC who is a SOLDIER trainee but has a secret connection to the Ancients. Another could be an OC who is a merchant in Midgar, dealing with the various gangs and Shinra's influence. And also, an OC who is a researcher studying the effects of Mako on the planet.
One idea could be that the OC is a powerful mage from a far - off land who crosses paths with Noctis during his journey. They initially clash due to different beliefs but gradually come to understand and support each other. Another could be the OC being a commoner who saves Noctis from a dangerous situation, and Noctis feels indebted to her and they form an unlikely bond.
One idea could be a crossover with another popular RPG like 'Dragon Age'. Imagine the characters from FF13 in the world of Thedas, dealing with the different races and magic systems there. Another idea is a crossover with a sci - fi universe like 'Mass Effect'. The technology and alien species in that universe would create a really unique setting for the FF13 characters. Or perhaps a crossover with a classic fantasy like 'The Lord of the Rings'. The FF13 characters could interact with hobbits, elves, and dwarves, which would be quite a sight.
A FF14 crossover fanfiction could involve crossing over with the 'Harry Potter' universe. The mages in FF14 could attend Hogwarts and learn different forms of magic. Or, a crossover with the 'Star Wars' universe. The Jedi and Sith powers could be compared and contrasted with FF14's dark and light magic. Also, a crossover with the 'Pokémon' world. The players in FF14 could capture and train Pokémon alongside their normal adventures.
A cool 'ff7 crossover fanfiction' idea could be to cross it with the 'Star Wars' universe. Picture Sephiroth as a Sith Lord, with his powerful abilities and dark charisma. He could face off against Jedi Knights. Or perhaps Aerith could befriend some of the more force - sensitive characters in the Star Wars universe. Another option is to crossover with the 'Mass Effect' series. The technology in Mass Effect could be an interesting contrast to the more magic - based elements in FF7. Characters like Tifa could interact with the alien species in Mass Effect.
One interesting idea could be changing the outcome of key battles. For example, if a character travels back in time, they might be able to prevent a certain loss in a fight, which could then change the entire course of the story. Another idea could be related to relationships. A character might go back in time to fix a broken relationship or to start a relationship earlier than it originally happened in the ff8 universe.
One idea could be Naruto being summoned into the world of FF14. He might initially be confused but quickly adapt his ninja skills to the new environment. For example, his ability to use chakra could be translated into a unique form of magic in FF14.
Another interesting concept is to have the chakra system from Naruto integrated into the FF7 universe. Maybe the materia could be enhanced by chakra, or characters could learn to use jutsu instead of magic. For instance, Aerith could learn some healing jutsu to add to her abilities.
Well, you could have an OC that is a skilled hacker who gets involved with the Phantom Thieves by accident. They might have a Persona that represents a famous code - breaker from history. Also, an OC who is a foreign exchange student from a country with a very different cultural background could bring in new elements to the fanfiction. Their Persona could be influenced by their home country's folklore. Maybe an OC who is a prodigy artist and uses their art skills to create powerful items in the Metaverse, with a Persona related to a great artist from the past.
You could have an OC that is a young witch who idolizes Bayonetta. She tries to copy Bayonetta's style and fighting techniques but often fails in a comical way at first. As the story progresses, she discovers her own unique way of being a witch. Or an OC who is a cursed object collector. This OC comes across Bayonetta when investigating a powerful cursed object and they end up working together to either destroy or control the object's power.