One way could be to create a crossover universe where Mordred from Fate Stay Night somehow ends up in the Naruto world. Maybe she could be a new kind of ninja with her own unique abilities based on her Fate Stay Night powers. For example, her sword skills could be translated into a new form of kenjutsu in the Naruto world.
In a fanfic with these elements, the plot could revolve around a threat that only Mordred, with her Fate Stay Night powers, can help the Naruto characters defeat. The Naruto characters might initially be suspicious of her, but as they see her in action and learn about her past, they start to trust her. Mordred, on the other hand, could learn valuable lessons from the Naruto world, such as the importance of teamwork which might be different from what she experienced in her own world. This kind of interaction between the two universes can create a really interesting and engaging fanfic.
Well, first, you need to think about the characters' personalities. Mordred is quite bold and headstrong in Fate Stay Night. In a Naruto fanfic, she might clash with some of the more traditional ninja clans due to her different upbringing. You could also consider how the magic system from Fate Stay Night could interact with the chakra system in Naruto. Maybe Mordred's magic could be seen as a very rare and powerful form of chakra manipulation that others in the Naruto world are both intrigued and a bit scared of.
A plot could be that Mordred is summoned by a powerful ninja as a last - ditch effort to fight against an ancient evil that has emerged in the Naruto world. This evil has powers similar to some of the powerful Servants in Fate Stay Night, so Mordred's expertise is needed.
One common theme is the clash of power systems. Since Naruto has chakra - based powers and Fate Stay Night has magic, seeing how these two different types of powers interact or conflict is often explored. For example, in many fanfics, Naruto might try to use his chakra to counter a magical attack from a Fate character.
One interesting Fate Stay Night Naruto fanfic is 'Naruto in the World of Fate'. In this fic, Naruto is somehow transported to the Fate Stay Night universe. It's really cool to see how his ninja skills interact with the magic and combat system in the Fate world. Another one could be 'Fate Servants in Konoha' which imagines what would happen if Fate's Servants showed up in Naruto's village.
The most common themes include the exploration of different cultures. Naruto has its own ninja culture, while Fate Stay Night has the mage and servant culture. Fanfics usually show how these two cultures clash and blend. Destiny is also a big theme. Given the importance of destiny in both series, in the fanfics, characters often question or try to change their fates. Moreover, self - discovery is a theme. Characters from both sides discover new aspects of themselves when exposed to the other world's situations and characters. This can lead to interesting character development throughout the fanfic.
I really like the fanfic 'Rin's Redemption'. It focuses on Rin's character development in a way that the original might not have fully explored. The plot is filled with twists and turns that keep you hooked from start to finish.
Love and friendship are also common themes. An OC could develop a deep friendship or even fall in love with Mordred. This relationship can be complicated by Mordred's status as a Servant and the events of the Holy Grail War. It can also be a source of character development for both the OC and Mordred. For instance, Mordred might learn about different forms of love and loyalty through her relationship with the OC, while the OC might grow in courage and determination as they get closer to Mordred.
One idea could be to have Naruto characters participate in the Holy Grail War. For example, Naruto himself could be a Servant, perhaps with his chakra being a unique form of mana. His skills like the Rasengan could be reimagined as powerful Noble Phantasms. Another idea is to put the Fate Stay Night characters in the Naruto world. They might have to deal with things like ninja clans and the politics of the hidden villages while also trying to find a way back to their own world.
One popular 'naruto and fate stay night fanfic' is 'Naruto in the World of Fate'. It combines the unique ninja elements from Naruto with the magic and servant system of Fate Stay Night. Another one could be 'Fate's Ninja', which often has interesting crossovers in terms of character interactions, like Naruto meeting Saber and having to fight together against a new threat that combines the evils of both worlds.
There's 'Fate's Ninja'. It focuses on how the ninja skills from Naruto's world can be combined with the magic and concepts in Fate Stay Night. The story has a lot of character development for both Naruto characters in the Fate universe and vice versa, showing how they learn from each other's worlds.
Power and its limits. When Naruto characters enter the Fate universe or vice versa, they have to figure out how their powers stack up. For instance, Naruto's huge chakra reserves compared to the magic in Fate Stay Night.