Well, you could have an OC that is a mage from a far - off land, like a desert kingdom, and they bring with them a whole new set of magical practices. For example, their magic could be based on sand and wind, which is very different from the usual European - style magic in the Fate Series. Or perhaps an OC who is a cursed artist. Their art has the power to come to life, but in a twisted way, and they get involved in the Grail War because they hope to find a way to break their curse. Also, an OC who is a detective - like mage, using their skills to uncover the secrets behind the Grail War and the true nature of the Servants.
An interesting concept for a Fate Series OC fanfiction could be an OC who is an artificial human created by a mad scientist mage. This OC has no memories of their creation but slowly discovers their inhuman abilities during the Grail War. They might have enhanced physical strength and the ability to quickly analyze and learn new magic. Another idea is an OC who is a spirit of a long - dead forest. In the modern world, the forest is mostly gone, but the spirit takes on a humanoid form to participate in the Grail War to protect the last remnants of nature. And then there's the idea of an OC who is a young mage apprentice who accidentally stumbles into the Grail War and has to quickly learn to survive and use their limited magic skills in creative ways.
One idea could be creating an OC who is a time - traveling mage from a forgotten era. They could have unique spells that interact strangely with the modern Fate world. Another is an OC who is a half - human, half - divine being, struggling with their identity in a world full of pure - blooded Servants and Mages. A third idea is an OC with the power to manipulate emotions, which causes chaos during the Holy Grail War as they can turn allies into enemies and vice versa.
One idea could be a crossover between Fate/Stay Night and another popular anime like Naruto. You could have the Servants from Fate interacting with the ninja world. For example, Saber could face off against Naruto in a battle of ideals. Another idea is a crossover with Harry Potter. Imagine the mages in the Fate universe collaborating with Hogwarts students to fight a common magical threat. Or a crossover with Attack on Titan, where the Servants help the Survey Corps in their fight against the Titans.
One idea could be creating an OC who is a time - traveling mage from a future where the Grail Wars have had catastrophic consequences. This OC could be on a mission to change the past to prevent the disasters. Another idea is an OC that is a hybrid of a Servant and a human, with unique abilities and a complex backstory that ties into the existing lore of Fate Grand Order. Maybe an OC who was experimented on by the mages in Chaldea and gained strange powers as a result.
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.
One idea could be creating an OC who is a mage from a long - lost family line. They could have a unique magic ability, like the power to manipulate time on a small scale during battles. This OC could get involved in the Holy Grail War, perhaps siding with a particular master from the original series and changing the course of some battles with their unforeseen powers.
Perhaps an OC who has a special power related to nature in a world full of high - tech. They could struggle to fit in at first but then find ways to combine their natural abilities with the tech - savvy of the Big Hero 6 team. For example, using plants to enhance communication devices or something like that.
One idea could be creating an original character (OC) who is a new villain in Gotham. This OC could have a unique power, like the ability to control technology. They would target Batman's high - tech gadgets and try to disrupt his crime - fighting efforts.
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.
Another type of 'oc fate fanfiction' is one where the oc is a unique Servant. Maybe they are a Servant created from a modern - day concept or a forgotten legend. Their abilities would be different from the traditional Servants, and their relationship with their Master would also be unique. For instance, an oc Servant based on the concept of 'Internet Fame' could have abilities related to information gathering and spreading, and their story could explore how they fit into the world of Fate.
One idea could be that the OC is a mage who has a special ability to communicate with all female servants on a deeper emotional level. This could lead to various adventures where they team up to solve mysteries in the Fate universe.
You could write a fanfiction that focuses on a side character and gives them a more prominent role. This character could have their own adventure or be involved in a sub - plot that ties into the main story in an unexpected way. It might also be interesting to write a time - travel based fanfiction within the 'A Strange Fate' universe, where a character goes back in time to change a crucial event.