Well, perhaps a plot where Percy discovers that being married to the Fates gives him the ability to see snippets of the future, but it's all jumbled up. He then has to work with the Fates to figure out how to use this new power properly. Also, there could be a story line where other gods are jealous of Percy's connection to the Fates through marriage and try to undermine him.
One idea could be Percy going on a quest that was pre - ordained by the Fates. He discovers that his every move is part of a larger plan they have for the demigod world. For example, he might be sent to retrieve an ancient artifact that holds the key to maintaining the balance between the gods and the Titans, and along the way, he has to face challenges that test his loyalty to the Fates' plan.
Well, a plot idea could involve Percy being cursed by the fates to forget his own identity. He then has to go on a journey to rediscover who he is while still fulfilling his duties as the champion of the fates. Along the way, he might meet old friends who don't recognize him at first, and he has to prove himself to them. Or perhaps the fates send Percy on a mission to prevent a prophecy from coming true that would destroy the entire demigod world. This would involve him traveling to different mythological places and facing powerful enemies.
Maybe Percy is chosen by the Fates to be their champion in a battle against an ancient evil that threatens to disrupt the very fabric of fate. He has to team up with some unlikely allies, like minor gods who are also concerned about the balance of fate. He would have to learn new skills and face challenges that test his limits.
Well, a plot could involve Percy being sent on a special mission by the Fates. Since they control destiny, this mission might be crucial for the balance of the entire demigod world. He could have to face enemies that are normally out of reach for regular demigods. Along the way, he discovers secrets about his adoption that change his perspective on his life and his role among his peers.
Maybe they start a family in a hidden part of the world. Percy could teach their children about his demigod skills and Calypso could pass on her knowledge of nature and magic. It would be a story full of family adventures and protecting their new life together.
Well, they could face issues like how to balance their heroic duties with their married life. For instance, Percy might get called away on a quest right when they planned a romantic dinner. Or perhaps in the fanfiction, they start a school for demigod children together as a married couple, which would bring its own set of comical and heartwarming situations.
An OC could be a half - human, half - dragon in the Fire Emblem Fates universe. They struggle to fit in either among the humans or the dragonkin. Their story could revolve around trying to find a place where they belong while also dealing with the powers that come with their unique heritage and the suspicion of both sides.
One idea could be a character from a different 'fate' in the Astoria world accidentally gets transported to the main character's 'fate' and causes chaos in their love life. Another could be a time - traveling plot where a character goes back in time to change an event that affected their relationship in the Kiss storyline.
One idea could be exploring an alternate timeline where the main character makes different choices at key moments in the game. For example, siding with a different faction from the start and seeing how the relationships and battles play out.
One idea could be a crossover with another popular RPG like Final Fantasy. Characters from Fire Emblem Fates could find themselves in a world filled with magic crystals and different races from Final Fantasy. They might have to team up with FF characters to fight a common enemy, like a powerful demon that threatens both worlds. Another plot could involve a crossover with a more modern - day setting, such as a post - apocalyptic world. The Fire Emblem Fates characters would have to adapt their combat skills and strategies to this new and harsh environment. They could meet survivors in this world who have different values and beliefs, leading to interesting character interactions.