One idea could be Percy having to face an ancient prophecy that only he, as the last of the seven, can fulfill. Maybe he has to journey to a long - forgotten realm and gather the lost powers of the other six demigods to defeat a new, powerful enemy.
Well, perhaps in the fanfiction, Percy discovers that being the last of the seven gives him some unique abilities that he has to learn to control. He could start having visions of the past and future of the demigod world, and he has to use these visions to prevent a catastrophic event from happening. He might also have to team up with some unexpected allies, like a group of minor gods who are also interested in the fate of the demigod world.
In this fanfiction, it could be interesting if Percy, as the last of the seven, is the only one who can enter a dangerous magical maze that holds the key to saving the world. Inside the maze, he encounters all sorts of challenges and traps that are specifically designed to test his skills and his will. He also has to deal with his own inner demons, as the weight of being the last hope for the demigod world starts to take a toll on him. Along the way, he might find some hidden secrets about the origins of the seven and their true purpose.
One idea could be exploring a different origin for one of the demigods. For example, making Annabeth's mother not Athena but a minor goddess, which would change her whole dynamic and the way she views herself as a demigod. Another plot could involve the seven demigods getting lost in a new, never - before - seen realm in the Underworld. This would test their survival skills and their ability to work together without the help of their usual allies. A third plot could be about a love triangle between two of the demigods and a new character that they meet during one of their quests, which would add an interesting layer of drama to their relationships.
Perhaps Percy discovers a hidden prophecy that involves him sacrificing something dear to him to save the demigod world once and for all. This could lead to a lot of internal struggle as he decides what to do. In the fanfiction, he could journey to places never before explored in the original series to find answers.
Another plot could involve a new threat emerging that is related to the events of 'The Last Olympian'. Say, some ancient power was awakened during the big battle but no one noticed at the time. A group of demigods, led by Percy, has to figure out what it is and how to stop it before it's too late. They might have to journey to some long - forgotten places and face new monsters along the way.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
One idea could be exploring Percy's life after the main events. Maybe he has to face a new threat that is related to an ancient prophecy that was overlooked. He could go on a journey with his old friends, like Annabeth, to discover the truth behind it.
A plot could be that Sally Jackson plants a lemon tree in her garden that turns out to be a gift from a minor goddess. The lemons from this tree have the power to give those who eat them the ability to see through illusions for a short time. Percy uses these lemons to his advantage when he is on a mission to retrieve a powerful artifact that is guarded by a monster that uses illusions to protect it.
Perhaps a fanfiction where Percy and Thalia are transported to an alternate dimension. In this new world, they have to figure out how to get back while also dealing with different versions of their friends and enemies. Thalia might have to face an alternate version of herself who has turned evil, and Percy could be the one to help her see the light again. It would be full of action, drama, and self - discovery.
A plot could involve Hera taking Percy on a journey through the past to show him the origins of the gods' power and how it relates to the current problems in the demigod world. This would give Percy a new perspective and knowledge that he can use to save the day. Or perhaps Percy accidentally stumbles upon a secret of Hera's that she's been hiding for centuries, and she has to enlist his help to keep it safe, all while other gods are trying to uncover it too.
Another plot idea could be that Percy discovers a hidden underwater civilization that is not related to Poseidon. This civilization has its own set of rules and powers. Percy has to navigate through their complex society and politics while also trying to convince them to help the demigods in a coming war against an ancient evil that is rising again. The underwater civilization could have unique magic and technology that the demigods have never seen before.
One idea could be that Percy has to face a new threat from Medusa's long - lost sister who has even more powerful petrifying abilities. He has to use his skills and some newfound knowledge about the Gorgon lineage to defeat her.