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.
A good 'Final Fantasy Sephiroth Crossover Fanfiction' should have a believable crossover concept. For example, if he crosses into a different universe, the rules of that universe should be well - defined and Sephiroth's presence should make sense within it.
Sephiroth is a central and complex character in Final Fantasy 7. He was once a celebrated SOLDIER, a powerful warrior in Shinra's military. However, he discovers the truth about his origin - that he was created through Jenova's cells. This revelation drives him insane. He then sets out on a path of destruction, believing he is a superior being. He wants to become a god and reshape the world according to his will, which leads to a series of events that form the main conflict of the game as the main characters try to stop his apocalyptic plans.
Another aspect is the emotional side. The OC could be written to have a romantic or platonic attraction to Sephiroth. If it's romantic, it would add a whole new layer of complexity to their relationship, with love and conflict intertwined. And if it's platonic, it might be a friendship that challenges Sephiroth's view of the world and his place in it.
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.
The plot is also crucial. It should not just be a simple love story but rather incorporate the rich lore of Final Fantasy. Maybe the OC is involved in the fight against the greater evil in the Final Fantasy universe, and Sephiroth plays a role in that struggle, either as an ally or an antagonist depending on the story's arc.
One idea could be that Sephiroth somehow gets transported to the feudal era of Inuyasha. He might initially be seen as a great threat due to his power. But as the story progresses, he could form an unlikely alliance with Inuyasha and his group against a common enemy, like a powerful demon that is even more menacing than any they've faced before.
Sephiroth's character is frequently developed as a complex villain. His backstory, such as his discovery of his true origins, can be delved into deeper in fanfiction. He can be shown as not just a one - dimensional bad guy, but someone with his own motives and reasons for his actions, which are often tied to his relationship with Cloud. For example, his envy or obsession with Cloud can be a driving factor in his character development.
One interesting storyline could be a redemption arc for Sephiroth. In this fanfic, Cloud might be the one to help him see the error of his ways. Maybe through their battles and interactions, Cloud starts to understand Sephiroth's tortured past and tries to guide him towards the light. This could involve them facing off against new threats together, with Sephiroth slowly learning to use his power for good instead of destruction.
One great Naruto x Final Fantasy fanfiction is 'The Ninja of Spira'. It combines the unique ninjutsu skills from Naruto with the magic and world - building of Final Fantasy. The story has an interesting plot where Naruto characters are transported to the world of Final Fantasy. It's a great read if you like crossovers that blend action and magic.
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.