The gods themselves could be interesting characters to include. For example, Poseidon could offer Percy more power or advice at crucial moments. Athena could also play a role, perhaps initially being an adversary because of her different goals, but later becoming an ally. Even minor gods like Hecate could be included. Her magic could be used to help Percy in situations where his normal powers aren't enough. Also, new characters created specifically for the fanfiction, like a powerful demigod from a previously unheard - of lineage, could add an element of surprise and freshness to the story.
A plot idea could be that Percy discovers a hidden underwater civilization that has been in stasis for centuries. This civilization has a powerful weapon that could either save or destroy the world. Percy has to navigate the politics and power struggles within this new society to either obtain the weapon for the good of the world or stop someone else from using it for evil. Also, Percy could lose his memory and end up in a normal human town. He has to rediscover his powers while also protecting the town from a series of mysterious attacks that are actually related to the world of the gods.
Another plot twist might be that Tartarus itself has a weakness that Percy discovers by accident. For example, he might notice that certain sounds or vibrations can disrupt the structure of Tartarus. This would completely change the game as he could then use this knowledge to his advantage, perhaps causing mini - earthquakes to distract or even harm the monsters that are after him.
Well, Percy himself is of course the main character. Annabeth would also be very likely to be there. Their relationship is a big part of the Percy Jackson series, and in a Tartarus - related fanfiction, she could be either with Percy from the start or trying to find a way to rescue him. Grover might also show up. His loyalty to Percy and his skills as a satyr could be useful in the dangerous environment of Tartarus.
One idea for a Percy Jackson famous singer fanfiction could be that a famous singer is actually a demigod in disguise. Maybe they use their music as a form of magic or to communicate with other demigods secretly. For example, their lyrics could hold hidden messages about upcoming quests or threats to the demigod community.
Well, it could be a really interesting and terrifying addition. Maybe it could be some kind of ancient monster that was locked away long ago in the world of Percy Jackson. It could be released by some dark magic or an evil demigod. The xenomorph's ability to adapt and its deadly nature would make it a formidable foe for Percy and his friends.
Well, in some fanfictions, Percy might use his water - controlling abilities. Since poison can be in liquid form, he could manipulate the water within the poison, perhaps separating out the harmful components. Another way could be through his demigod powers, which might give him an innate resistance or control over harmful substances like poison.
In a Percy Jackson in World War II fanfiction, Percy might have to team up with some of the Allied soldiers. His sword fighting skills would be a great asset. He could also communicate with sea creatures to get information about enemy movements at sea. And perhaps he'd meet other demigods from different parts of the world who were also drawn into the war for various reasons.
Typhon in Percy Jackson fanfiction can be a great vehicle for exploring the concept of fear. His sheer size and power are terrifying. Writers may show how the characters overcome their fear of Typhon. It could be through the power of friendship, like Annabeth coming up with a brilliant plan and giving Percy the confidence he needs to face Typhon, or it could be Percy finding inner strength he didn't know he had.
One interesting aspect in Percy Jackson and Demeter fanfiction could be the relationship between Demeter's powers over nature and Percy's adventures. For example, Demeter could use her powers to help Percy in a quest that involves a lot of natural elements like a forest that has been corrupted. She might be able to manipulate the plants to guide him or provide him with resources he needs.