Perhaps a plot where Ritsuka's harem has to work together to defend a certain area from powerful enemies in the 'Fate Grand Order' universe. The harem members might have different strategies based on their unique abilities, and Ritsuka has to manage them all.
Jeanne d'Arc is also frequently seen in such fanfictions. Her noble and kind nature makes her a great addition to Ritsuka's harem. And then there's Scathach, with her powerful and mysterious persona, she can bring a lot of interesting dynamics to the harem in the fanfiction.
A possible plot could be Scathach's exploration of the modern world. Since she is from an ancient time, her reactions to modern technology, culture, and society can be a great source of interesting storylines. She might be initially confused by things like smartphones or cars, but then gradually learn to use them in her own unique way. This could also lead to humorous situations, like when she tries to order food at a fast - food restaurant for the first time.
A common trope is the 'protective harem'. In Fate Grand Order harem fanfiction, the Servants in the harem often feel the need to protect the Master (the protagonist). This can lead to some interesting scenarios where they compete to be the best protector. Also, the 'unexpected bond' trope is quite popular. It's when two characters who seem very different at first end up having a deep connection within the harem. For instance, a heroic Servant and a more villainous - like Servant might form an unexpected bond over their shared love for the Master.
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 interesting concept could be the exploration of different Servant backstories in more depth. For example, delving into the pre - summon experiences of a Servant that might not be fully covered in the game. Another could be alternative versions of the Holy Grail Wars, with different rules or participants. Also, the fanfiction might explore the relationships between the Masters and Servants in unique ways, like how they interact outside of battle situations.
In some 'fate grand order gamer fanfiction', the focus could be on a group of gamers who compete in a special in - game tournament. Each gamer has their own unique strategy and team of servants. One gamer might use a team of underrated servants and through clever tactics, manages to defeat opponents with more popular and powerful servants. This shows how creativity can play a big role in the Fate Grand Order gaming world as depicted in fanfiction.
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.
A crossover with the Naruto universe could also be exciting. Imagine Servants like Archer using their skills against ninjas. Naruto characters might be intrigued by the concept of Servants and their powers. It could lead to a story where they exchange combat techniques and learn from each other.
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.
Her motherly nature. In many fanfictions, Raikou's motherly side is explored, especially in relation to other servants or the Master. She can be very protective.