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.
Maybe Percy has to deal with other demigods who are jealous of his special connection to the Fates. They could try to undermine his quests or turn other demigods against him. This would create a lot of internal conflict within the demigod community and force Percy to prove himself not just as a son of the Fates but also as a worthy ally to his fellow demigods.
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.
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.
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 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.
One interesting plotline could be Percy having to deal with the complex powers and expectations that come with being the 'Son of the Fates'. Maybe he has visions of different possible futures and has to figure out how to navigate them to save his friends and the world. Another could be his interactions with other demigods who are either in awe or afraid of his new status.
One idea could be Percy having to struggle with the dark reputation that comes with being Lucifer's son while trying to prove he's not all bad. Maybe he forms an unlikely alliance with some angels who initially distrust him but later see his good side.
One idea could be Percy having to prove himself in the Underworld. Since he's the son of Tartarus, he might face unique challenges from the other denizens who fear or distrust him. Maybe he has to compete in some sort of underworldly tournament to gain respect.
A really cool plot could be Percy getting caught in an alternate dimension where Ares is the main god in charge. He has to find a way to survive in this new world, where the rules are different and he's seen as an outcast. Percy would need to use his wits and skills to navigate this strange place and find a way back home.
A great plot idea would be Percy getting trapped in one of Daedalus' old mazes. He has to use his wits and the skills he's learned as a demigod to find his way out. Along the way, he encounters old traps and puzzles set by Daedalus himself. This could also be a chance for Percy to meet the spirit of Daedalus within the maze and learn some valuable lessons from him. Or perhaps Percy has to team up with other descendants of Daedalus to solve a mystery that has been plaguing their family for generations.
A possible plot could be a competition among the demigods where Percy, as a 'Son of Ares' in this fanfiction, has to prove himself against other powerful demigods. The competition could include tasks like combat, strategy, and survival challenges. Along the way, Percy could learn more about the Ares - like qualities within himself and also form new alliances or rivalries.