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.
The OC could be a new type of hero with a unique power source. The female servants are initially skeptical but then gradually come to respect and work with the OC. They could fight together against a common enemy that threatens the balance of the Fate world. The relationships between the OC and each servant could develop in different ways, some might become close friends, while others could have a more mentor - mentee relationship.
Medea is also a great option. Her complex personality, including her dark past and her powerful magic, can add depth to the fanfiction. The OC could either be an ally trying to redeem her or someone who has to face her as an enemy.
One interesting fanfiction in this category might be 'A New Adventure'. It has a unique OC who forms deep and diverse relationships with the female servants. The story is well - written, with great character development.
The appeal lies in the unique relationships that can be formed. The OC can bring a fresh perspective and new storylines to the existing Fate Stay Night world. It's exciting to see how they interact with the well - known female servants.
The fem oc could be a healer who is assigned to take care of Naruto after a particularly tough battle. She has a very calm and nurturing personality. As she heals him, they start to share stories about their pasts. Naruto is intrigued by her selfless nature and she is inspired by his determination. This leads to a slow - burning relationship as they get to know each other better.
A plot could involve the fem alien being in danger on Earth and the OC coming to her rescue. This could lead to a bond between them. Maybe the OC discovers that the fem alien has special powers that she needs to hide from the wrong people on Earth. They then have to work together to keep her safe and in the process, they fall in love.
One plot idea could be that the OC is a new recruit in the TF2 team and has an instant attraction to the Fem Pyro. They start off as friends, but as they go on various missions together, they gradually fall in love. For example, during a battle on a snowy map, the OC gets trapped and the Fem Pyro risks her life to save him, which deepens their bond.
One idea could be that the fem oc is a new camper at Camp Half - Blood with a unique power related to nature. She and Percy have to go on a quest together to save a forest that is being poisoned by a mysterious force. Along the way, they discover that their powers work better together and start to develop feelings for each other.
A plot could involve the OC being a lost soul who accidentally wanders into Scathach's realm. Scathach, being intrigued by this strange being, decides to keep the OC around. The OC gradually adapts to this new world and starts to learn Scathach's ways. They could then get involved in a battle against a common enemy, perhaps an ancient evil that threatens both their worlds. The OC might also introduce Scathach to new concepts from their own world, leading to a cultural exchange of sorts within the story.
One idea could be that the OC discovers All Might in his feral state and tries to help him regain his humanity. Maybe the OC has a special power that can soothe his wild nature. For example, the OC's power could be related to nature, like the ability to communicate with animals. They use this power to connect with All Might on a deeper level and slowly bring him back to his normal self.
One plot idea could be that the fem OC is a new mutant who Emma Frost takes under her wing to train. They start with a rocky relationship due to differences in their personalities but gradually grow to respect and care for each other.