Well, these kinds of fanfictions often explore different aspects of the Servant - Master relationship. Since it's an SI OC Servant, the story can take a very personal turn. The author can play with the idea of how a modern - day person, if inserted into the FGO world as a Servant, would react to the historical and mythological figures around them.
One of the things that makes it special is the freedom to create. Writers can design their own Servant with any kind of powers, appearance, and personality. It's like creating a brand - new character in the rich world of Fate Grand Order.
One interesting Fate Grand Order OC Servant fanfiction could be about a new Servant with the power of time manipulation. This Servant could be from a lost era and has unique abilities that change the course of battles in the Holy Grail War. Their backstory might involve a tragic past related to the misuse of time magic, which makes for a great plot device.
One interesting story could be about an original character (OC) who has a unique ability and gets involved in the complex plot of Fate Grand Order. For example, an OC with time - controlling powers that changes the outcome of a certain battle.
First, you need to create your OC Servant. Decide on their class, like whether they're a Lancer or a Rider. Then, think about their origin. Are they from a historical period, a fictional world, or a lost civilization? After that, work on their abilities. It should be something unique and relevant to their origin. For example, if they're from a water - based civilization, they might have water - related powers.
First, know the lore of Fate Grand Order well. This includes the different servants, their abilities, and the overall world - building. Then, create an interesting OC with a distinct personality, backstory, and powers. For example, an OC who is a half - human half - spirit with the power to communicate with nature spirits.
One interesting SI (Self - Insert) fanfiction could be where the SI has a unique ability that changes the course of the story. For example, an SI with the power to manipulate time might prevent a major character's death and thus completely change the narrative. It adds a whole new layer of creativity to the Fate Grand Order universe.
When writing, focus on the details. Describe how your SI feels when they first see a Servant in person. How do they adapt to the strange world of Fate Grand Order? You can also draw inspiration from other fanfictions, but make sure to put your own spin on it. And always keep in mind the tone of the Fate Grand Order universe, whether it's dark and serious in some singularities or more light - hearted in others.
One common theme is power dynamics. The OC often has to navigate their relationship with powerful servants, who may have different levels of loyalty or attraction. For example, in some fanfics, a servant might initially be dismissive of the OC but later become part of the harem as they see the OC's growth or hidden strength.
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.