A great concept for Final Fantasy XV fanfiction is to focus on the relationships between the characters. You could write about how Prompto deals with his insecurities and how his friends help him. Or perhaps a story about Gladio's leadership and how he guides the group. You could also do a time - skip fanfiction, showing what happens to the characters years after the end of the game, like how they rebuilt Lucis.
Some interesting fanfiction ideas could involve crossovers. For instance, a crossover with another Final Fantasy game, where characters from Final Fantasy XV meet those from Final Fantasy VII. They could exchange fighting techniques or stories about their respective worlds. Another idea is to create a fanfiction based on the side characters in Final Fantasy XV. Maybe tell the story of Cindy and her daily life at the garage, or the adventures of Iris in a more detailed way.
One idea could be exploring the backstories of the main characters in more depth. For example, Noctis' training as a prince and his relationship with his father before the events of the game. Another could be a fanfiction set in an alternate universe where the Astrals have different roles or relationships with the humans. Maybe a story where Noctis and his friends have to face a new, unexpected threat that wasn't in the original game.
One interesting concept could be a crossover of the magic systems. In Final Fantasy XV, there's the use of elemental magic and powerful spells. In Naruto, there's ninjutsu. A fanfiction might explore how a character from one universe adapts to the other's magic. For example, a Naruto character learning to use the warp - strike ability from Final Fantasy XV in a battle. Another concept could be the interaction of the different races. The elves in Final Fantasy XV and the various clans in Naruto could have some really unique interactions, like how the Uchiha clan's sharingan might react to the magic - using races in Final Fantasy XV.
One interesting crossover could be the use of magic spells from 'Harry Potter' in the world of 'Final Fantasy XV'. For example, a character from 'Final Fantasy XV' might learn the Patronus Charm to fend off daemons. Another could be the appearance of Hogwarts - like buildings in the 'Final Fantasy XV' landscape. Maybe Noctis and his friends could attend a magical school similar to Hogwarts.
A possible fanfic could explore the concept of the crystal in Final Fantasy XV and the Fayth in Final Fantasy X. Maybe the crystal's power has some sort of connection to the Fayth, and characters from both games have to figure out how to use this connection to restore balance. This could involve a journey across both worlds, with characters learning about each other's cultures and histories along the way.
One idea could be Noctis traveling back in time to prevent the fall of Insomnia. He could use his knowledge of future events to stop the Niflheim invasion before it starts. Maybe he teams up with his father and the Crownsguard in their prime to fortify the city's defenses.
A possible crossover aspect is the world - building. The post - apocalyptic world of 'owari no seraph' and the more fantastical world of 'Final Fantasy XV' could merge. Maybe the characters from 'Final Fantasy XV' end up in the world of 'owari no seraph' and have to deal with the vampire - human conflict. They could bring their own technology and magic, which would change the balance of power in the 'owari no seraph' world.
One idea could be exploring the backstories of the minor characters. For example, the SeeD trainees who don't get much spotlight in the game. Another could be a 'what if' scenario, like what if Squall and Rinoa didn't end up together? It could also be interesting to write about the world of Final Fantasy 8 from the perspective of an ordinary citizen living in one of the cities, dealing with the sorceress wars and the chaos that ensues.
Well, I'm not sure specifically which ones are the 'good' ones as lemon fanfiction often contains inappropriate content. However, if you're interested in regular 'Final Fantasy XV' fanfiction, there are many great ones on platforms like FanFiction.net that focus on the characters' adventures, relationships in a non - inappropriate way, like those exploring Noctis and his friends' journey to save the kingdom.
A great Naruto Final Fantasy fanfiction idea is to combine the magic systems. In this story, shinobi could learn to use Final Fantasy - style magic, like black magic for offensive spells and white magic for healing. Or perhaps a plot where the Akatsuki is after a powerful crystal from the Final Fantasy world that could grant them ultimate power. Also, a fanfic about a character from Naruto traveling through different worlds of Final Fantasy, facing the challenges and enemies in each world.
One idea could be to create an OC who is a mage from a long - lost tribe in Ivalice. They could have unique spells that are based on ancient tribal magic. Another idea is an OC that is a sky pirate with a mysterious past, perhaps related to the great airships of the game. Or an OC that is a knight trying to restore an old code of honor in a time of political unrest in the game's world.
One idea could be a crossover with the 'Harry Potter' universe. Squall could be a wizard, and his gunblade could be enchanted. Another could be a crossover with 'Star Wars', where the characters from Final Fantasy 8 are in the middle of the galactic conflict. Maybe Laguna could be a Jedi - like figure.