Well, for 'fate stay night crossover fanfiction', a crossover with 'The Lord of the Rings' could be epic. Picture the Fate servants in Middle - earth, fighting alongside or against the Fellowship. The different races and cultures in Middle - earth would provide a rich backdrop for the Fate characters. And a crossover with 'Bleach' is also a possibility. The Soul Society and the powers of the shinigami could interact in unique ways with the powers in the Fate world.
A cool 'fate stay night crossover fanfiction' idea might be a crossover with 'Final Fantasy'. The different classes and magic systems in Final Fantasy could blend well with the Fate universe. For example, a character from Fate could learn the job classes from Final Fantasy. Also, a crossover with 'Persona' could be interesting. The Velvet Room and the concept of personas could be integrated into the Fate world, adding a new layer of mystery and power to the story.
One interesting plot idea could be that the Servants from Fate Stay Night end up in the Naruto world. For example, Saber could team up with Naruto. Saber's noble and just nature would blend well with Naruto's determination to protect his village. They could face off against common enemies like Orochimaru, who might be interested in the power of the Servants. Another idea is that the concept of chakra in the Naruto world could interact with the magic in Fate Stay Night. Maybe a mage from the Fate universe tries to study chakra and finds a way to combine it with their own magic system, creating a whole new type of power. A third plot could involve the Holy Grail War taking place in the Hidden Leaf Village. The ninjas would be both intrigued and cautious about this strange new event, and the Servants would have to navigate the politics and unique environment of the village while fighting for the Grail.
One idea could be that Saber from 'Fate Stay Night' gets transported to the world of 'Frozen'. She could be mistaken for a powerful sorceress. Elsa might initially be wary of her but then realize they both have a connection to magic that they need to control. Another plot could involve Shirou being in Arendelle and using his skills to help build things, while also getting caught up in the drama between Anna and Hans. Maybe he could use his projection magic to create something that helps save the day in Arendelle.
One interesting idea could be exploring different routes for the characters. For example, what if Shirou had chosen a different Servant at the start? Another could be delving deeper into the backstories of the Servants, like revealing more about their lives before they became heroic spirits. Some fanfictions also play with the concept of alternate universes, where the rules of the Holy Grail War are changed completely.
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.
Perhaps Shirou from Fate Stay Night could find himself in the Re Zero world. He might use his skills as a mage and his determination to help Subaru in his quests. Their different outlooks on life and combat could lead to some interesting character development as they learn from each other.
A crossover with the Persona series is also quite popular. The themes of the inner self and combat against otherworldly entities in both series can be blended together. The characters from Fate Stay Night could potentially enter the Metaverse from Persona and interact with the Persona users. This could lead to some really cool battles and character development.
Another idea is to create a story where the rules of the Grail War are changed. For instance, instead of seven Servants, there are only three, and they have to complete different tasks to win. This would completely change the dynamics of the story and lead to new and exciting interactions between the characters.
One interesting concept could be how the gamer elements interact with the existing Fate Stay Night universe. For example, the protagonist might have a gamer interface that shows stats for the Servants, which could add a new layer of strategy to battles.
A possible plot for this crossover fanfiction could be centered around the concept of the 'ideal'. In Fate Stay, each Servant has an ideal they fight for, and in RWBY, the characters also have their own beliefs and goals. So, a story could be crafted where the characters from both universes have to compare and contrast their ideals. Maybe some of the Fate Stay characters are confused by the concept of the Grimm and the Huntsmen/Huntresses' role in RWBY, while the RWBY characters are intrigued by the Servant - Master relationship in Fate Stay.
Another idea is an OC gamer who creates a virtual reality game based on Fate Stay Night. But then something goes wrong, and the game world and the real Fate Stay Night world start to merge. This could lead to all sorts of interesting scenarios, like the OC having to team up with in - game characters to fix the mess while also dealing with the power struggles in the Fate universe.