A plot could involve Sephiroth being summoned accidentally by Orochimaru. Orochimaru wants to use Sephiroth's power for his own evil plans. However, Sephiroth is not one to be controlled. Naruto and his friends get caught in the middle. Naruto senses that there is some good in Sephiroth deep down, just like he believed in Sasuke. So he tries to reach out to Sephiroth. Meanwhile, Sephiroth is trying to figure out how to get back to his own world and is also intrigued by Naruto's strange power of the Nine - Tails.
Well, perhaps in this crossover, Sephiroth is a rogue ninja from a far - off land that has powers similar to his in the Final Fantasy world. He starts causing destruction in the Hidden Leaf Village. Naruto, being the hero, decides to face him. Along the way, they discover that their powers have some strange similarities. For example, Sephiroth's sword techniques could be compared to some of the advanced sword - using ninja in the Naruto world. And they might end up having to team up against a greater evil that emerges because of Sephiroth's arrival.
One possible plot could be that Sephiroth, with his superhuman abilities and thirst for power, somehow ends up in the Marvel universe. The Avengers initially mistake him for a new, extremely dangerous threat. They try to fight him but quickly realize his power level is off the charts. Then, they might try to find a way to send him back to his own world while Sephiroth, intrigued by the power sources in the Marvel universe like the Infinity Stones, tries to get his hands on them.
Naruto would probably be very curious about Sephiroth. He'd likely try to be friendly at first, asking a lot of questions. Sephiroth, on the other hand, would be more aloof and might see Naruto as a nuisance or a potential threat. But as time goes on, Naruto's determination might start to intrigue Sephiroth.
The most interesting plot point could be the clash of ideologies. Naruto, who stands for hope, friendship and protecting the weak, is a fan of Sephiroth, who represents power, destruction and self - centeredness. As Naruto tries to understand Sephiroth more, he starts to question his own beliefs. Does power always have to be used for good? Can someone as evil as Sephiroth have a redeeming quality? This internal struggle within Naruto, along with the external reactions of his friends and the ninja world, would make for a very engaging fanfiction.
One idea could be that Sephiroth somehow gets transported to the RWBY world. He might initially be seen as a threat, but then the characters realize he has knowledge that could help against a new, powerful Grimm. For example, his combat skills and his understanding of magic - like materia in his world - could be adapted to the Dust - based magic in RWBY.
Well, it could be about Sephiroth using his incredible combat skills from Final Fantasy in the world of Attack on Titan. Maybe he teams up with the Survey Corps to take on the Titans. He might use his Masamune sword to slice through the Titans' nape with ease, bringing a new level of badassery to the fight against the Titans.
One interesting Naruto Sephiroth fanfiction could be about Sephiroth somehow ending up in the Naruto universe and having to adapt to the ninja world. Maybe he teams up with Naruto to fight a common enemy. Another could involve Naruto learning some of Sephiroth's combat techniques and incorporating them into his own style.
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.
Well, it could be that Naruto is reborn as a sort of hybrid of himself and Sephiroth. His appearance might change slightly, with some of Sephiroth's features. In the story, he might have to learn to control the new powers which are far more destructive than his normal chakra - based abilities. And his friends, like Sasuke and Sakura, would be both confused and worried about this new Naruto.
One possible plot could be that Naruto has to go on a special mission with Kurenai. They might be sent to a hidden village where they discover a new type of jutsu that is being misused. Kurenai's genjutsu skills and Naruto's rasengan could be combined in unique ways to fight against the villains using this jutsu.
One possible plot could be that Riddick somehow gets transported to the Naruto universe. He could initially be seen as a threat, but then he teams up with Naruto and the others to fight a common enemy, like a new powerful Akatsuki member who has powers similar to some of the creatures in Riddick's world. Riddick's combat skills and his ability to see in the dark could give the Naruto gang an edge in battles.