One idea could be a story where Percy has to team up with a minor Greek god, like Hypnos, to defeat a new threat that's causing nightmares across the demigod world. Another could be a fanfic exploring what would happen if Percy was sent back in time to the age of the original Greek heroes and had to prove himself among them.
A great plot for a Percy Jackson and the Greek Gods fanfiction could be a situation where the gods are all cursed to lose their powers one by one. Percy, along with his friends, has to figure out who is behind the curse and how to stop it. They would have to journey through various mythical places, face old enemies in new forms, and maybe even make some unexpected allies among the minor deities. This would be a very action - packed and full of mystery, as they try to save the Greek gods and, in turn, the world as they know it.
Perhaps Percy could have a dream during Greek class about an upcoming prophecy related to the class. In the dream, he sees that a certain ancient Greek artifact hidden in the school is going to be discovered, and it will either bring great danger or great power. So, he spends the rest of the class trying to figure out how to stop or find it first. Also, he could get into an argument with a teacher who doesn't believe in the real existence of the Greek gods, but Percy has to prove it without revealing his true identity as a demigod.
Well, a great plot could involve Percy being transported to the Norse realm and having to prove himself to Odin. He might have to participate in a series of trials that are designed for Norse heroes. Or perhaps he gets caught in a feud between different Norse factions and has to use his wits and powers to bring peace. He could also discover a connection between the Greek and Norse pantheons that no one knew about before.
One idea could be Percy having to face a new, powerful enemy that is a threat to his newfound position as king of the gods. This enemy could be a primordial being that has been awakened. Another plot could involve Percy trying to reform the rules among the gods, which causes a lot of internal conflict as the other gods resist change. And perhaps Percy discovers a long - lost prophecy related to his kingship that changes everything he thought he knew.
One idea could be Percy having to team up with an Egyptian demigod to stop a common enemy that is causing chaos in both Greek and Egyptian mythological realms. Maybe a powerful monster that is using the powers of both mythologies to grow stronger.
A possible plot for this fanfiction is that the curse makes Percy lose his memory bit by bit. He forgets his friends, his past adventures, and even his own identity. As he struggles to figure out what's wrong with him, he starts having strange visions that are both a clue to the curse and a danger in themselves. Maybe the gods who cursed him are trying to erase him from existence, and he has to rely on his instincts and the few remaining memories to fight back. He might meet new characters who are either trying to help him or are part of the gods' plan to keep him cursed.
A possible plot could be that Percy is summoned to Japan by the Shinto gods to help stop an ancient evil that is threatening both the Greek and Shinto worlds. This evil could be a powerful demon that has the ability to disrupt the balance between the two pantheons.
One idea could be exploring a new prophecy that involves Percy and his friends having to team up with some of the lesser - known gods. This would introduce new characters and powers into the story.
Perhaps Percy is framed for a crime against the gods and has to fight them while also trying to prove his innocence. He could travel to different realms in the process, seeking evidence and allies. Along the way, he might learn some dark secrets about the gods that could change his perspective on them forever.
A really interesting plot would be if Percy lost his memory and ended up in a mortal town. He has to figure out who he is on his own while still being hunted by some old enemies. The gods are aware of his situation but can't interfere directly because of some ancient rule. So Percy has to rely on his instincts and any small clues he can find about his past to get back to his normal self and his life at Camp Half - Blood.
Perhaps a fanfiction where the New Gods create a sort of competition for demigods. Percy enters this competition and discovers that there are rules he's not used to, and he has to use his wits and skills in new ways to win. And along the way, he makes some unexpected allies among the new gods.