A potential storyline could be a battle - royale - style plot. Sephiroth and Rias are forced to participate in a tournament in a neutral dimension. They have to fight against various powerful opponents. Along the way, they learn about each other's fighting styles and motives. This could lead to an alliance between them as they realize they have a better chance of winning together. And in the end, they might face a final boss that is a threat to both their existences.
In this crossover fanfiction, perhaps Sephiroth is brought into Rias' world. Rias' peerage might initially be very wary of Sephiroth. However, his skills in combat and his knowledge of magic could prove useful. Rias could see potential in him and try to sway him from his darker path. They might go on adventures together, facing off against powerful devils and other threats, and in the process, a unique bond forms between them that is a mix of friendship and mutual admiration.
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.
In a Naruto - Rias' peerage fanfiction, the story might focus on how Naruto's chakra system interacts with the devil's power. For example, his ability to sense chakra could be enhanced or changed when combined with devilish senses. Also, his relationship with the members of the peerage would be interesting. He could form strong bonds with some, like Kiba in Naruto's world, he might get along well with the werewolf in Rias' peerage.
A fanfiction could explore the relationships between Naruto, Rias, and Akeno in a more character - driven way. For example, Naruto might be intrigued by the different social structures in their world compared to his. Rias could be fascinated by Naruto's growth from an outcast to a hero. Akeno, on the other hand, might be interested in Naruto's combat techniques. They could start as strangers but gradually develop deep friendships or even more complex relationships as the story progresses.
One popular sephiroth crossover fanfiction might be one where he crosses over into the Final Fantasy VII Remake universe in a different timeline. This can create interesting storylines as he interacts with the new versions of characters.
Another theme could be the cultural differences between the two universes. The Final Fantasy world has its own set of values, and the Sekirei world has its own. Fanfiction might play with how characters from these different cultures interact and adapt. For example, Sephiroth might find the concept of Sekirei pairs very strange at first. It can lead to interesting character development and relationship building within the story. And this often makes for an engaging read as the author tries to blend these two very different worlds together in a believable way.
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.
Inuyasha would probably be very wary of Sephiroth at first. Inuyasha is used to dealing with demons and his own set of problems in his world. Sephiroth's otherworldly power and cold demeanor would make Inuyasha see him as a potential threat. He might even attack first out of instinct.
One great Cloud x Sephiroth fanfiction is 'A World Remade'. It beautifully weaves a complex relationship between them, exploring their shared past and a possible future together. The writing is quite engaging, with detailed descriptions of their emotions and the world they inhabit.