Perhaps the characters swap worlds. Cloud wakes up in Hyrule, confused but ready to fight. He teams up with Zelda to stop Ganondorf, who has somehow acquired some of Shinra's technology. In reverse, Link could end up in Midgar, where he uses his bow and arrow skills to help the members of AVALANCHE in their fight against Shinra. They could learn from each other's combat styles and values, leading to an interesting dynamic.
Cloud and Link would have very interesting interactions. Cloud is a brooding, complex character with a lot of inner turmoil, while Link is often more of a silent hero. Cloud could be intrigued by Link's ability to face danger without hesitation and with such a pure heart. Link, on the other hand, might be curious about Cloud's past and his experiences with the Jenova cells. Their different fighting styles could also lead to some great action scenes where they learn from each other.
Another unique aspect is the reinterpretation of the 'Final Fantasy 7' story. In a crossover fanfiction, the main plot of 'Final Fantasy 7' can be twisted in new ways. Maybe Sephiroth has a different goal because of the influence of another universe's antagonist. This can breathe new life into the familiar 'Final Fantasy 7' narrative and give readers a fresh perspective on the story they already know.
Friendship and loyalty are often themes. In crossovers, the bonds between the Final Fantasy 15 characters are tested and strengthened. They might form new alliances in the new world they cross into, but their loyalty to their original friends from Final Fantasy 15 remains important. This theme helps to create emotional connections in the fanfiction.
One great 'Final Fantasy Sephiroth Crossover Fanfiction' is 'Sephiroth in Another World'. It's really interesting as it takes Sephiroth and throws him into a modern - day Earth setting. The way the author describes his confusion and then his gradual adaptation is quite engaging.
Maybe Zelda herself could be transported to the Avengers universe. With her wisdom and magic, she could assist the Avengers in different ways. She could use her magic to heal the wounded Avengers or help Tony Stark understand some ancient technology that has similarities to her own world's tech. She could also provide strategic advice based on her experience dealing with Ganon in her own realm.
One idea could be that Link, from Legend of Zelda, somehow gets transported to the Naruto universe. He might initially be mistaken for a strange shinobi with his unique green tunic and hat. Link could use his combat skills, like swordsmanship and shield defense, to team up with Naruto and his friends against common enemies, such as the Akatsuki who are after powerful artifacts. Maybe the Ocarina of Time has some sort of power that the Akatsuki wants, and Link has to protect it while in this new world.
One common theme is the clash of different worlds. For example, when Final Fantasy VII characters enter a different game universe, there's often a struggle to adapt to new rules and cultures.
One common theme is the exploration of different power systems. Since 'Final Fantasy XIII' has its unique l'Cie powers, when crossed with other franchises, comparing and combining these powers is interesting. For example, if crossed with 'Pokemon', how would the l'Cie powers interact with Pokemon abilities?
One common theme is the clash of cultures. When Noctis is taken to another universe, like in a crossover with a modern - day Earth setting, his own values and the way of life from his world in 'Final Fantasy' are different from what he encounters. Another theme is power comparison. For example, when he's in a world with superheroes or other powerful beings, how his magic and combat skills stack up.