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.
Another idea is to explore the relationship between the Norse gods and the Greek demigods in a fanfiction. Maybe the Norse gods are intrigued by Percy's powers and want to test him, or perhaps they offer him a quest in the Norse world. This could lead to Percy having to adapt to the different rules and challenges in the Norse realm.
Another interesting plot could involve Percy being hunted by both Greek and Norse monsters because he is an anomaly. He then has to team up with some unexpected allies, like a Norse dwarf and a Greek nymph, to fight back. As he does this, he uncovers secrets about his mother that change his whole perspective on his family.
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.
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.