A possible fanfiction could focus on the concept of the Holy Grail in Fate Stay Night being in Westeros. Different characters from Game of Thrones, like Daenerys, might see it as a means to achieve her rightful claim to the Iron Throne. Meanwhile, the mages from Fate Stay Night could be involved in the political intrigue, trying to either protect or use the Grail for their own purposes.
One idea could be a crossover where characters from Fate Stay Night are transported to the world of Game of Thrones. For example, Saber could be a powerful knight in Westeros, facing off against the likes of Jaime Lannister. Another idea might be that the magic system from Fate Stay Night is introduced into the Game of Thrones universe, causing chaos among the different houses as they vie for control of this new power.
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.
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.
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.
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.
Another interesting plot might be a 'what if' scenario. What if Shirou had to enter Rider's world, like the world she came from before being summoned in Fate Stay Night? He would be completely out of his element, and Rider would have to be his guide. This could lead to many comical and heart - warming moments as Shirou tries to adapt and they grow closer.
One idea could be an OC who is a gamer in the modern world suddenly gets transported into the Fate Stay Night universe during the events of the opening sequence. They could use their gaming knowledge, like strategic thinking and quick reflexes, to survive and make an impact on the Holy Grail War.
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.
First, do a lot of research on both universes. Know the characters, their motives, and the rules of each world. For example, understand the complex politics in Game of Thrones and the magic and servant system in Fate Stay Night. Then, find an interesting concept for the crossover, like what if a Fate Stay Night character was inserted into a key moment in Game of Thrones history. Make sure to keep the characters in - character, so if you write about Shirou in Westeros, he should still have his values and ideals, just adjusted to the new setting.
Another idea is the ability to hack the Grail system. In a fanfiction, the character could have hacker - like skills in the magical world. They might be able to change the rules of the Grail War, such as altering the summoning conditions for Servants or even adding new rewards. This would create a whole new storyline full of twists and turns as other characters react to these changes.