In some fanfictions, the plot could revolve around the half - robot being hunted by a secret organization. Percy gets involved and has to protect it. They go on a journey to find a safe place for the half - robot. Another idea is that the half - robot has a unique power that can only be unlocked by Percy's blood or something similar. And then there could be a plot where the half - robot is an experiment by a rogue demigod, and Percy has to put a stop to the unethical experiments and save the half - robot.
Well, a cool plot could be where the half - robot is a creation of Hephaestus gone wrong. Percy discovers it and has to figure out how to either fix it or stop it from causing chaos. It could also be a plot where the half - robot has a connection to Percy's past, like it was created using some of his essence from a past adventure. Or perhaps the half - robot is from a different dimension and Percy has to help it get back home while dealing with the problems it causes in his world.
It could be a rogue god who sees the half - robot as a threat to the natural order. They might try to destroy it because they don't like the idea of a half - human, half - machine being in the world of demigods. Another possibility is a powerful Titan who was awakened and wants to use the half - robot's technology for their own evil purposes. Maybe the half - robot has some sort of power source that the Titan desires.
Another plot could involve the Earthshaker being awakened accidentally. This causes chaos not only on Earth but also in the Underworld. Percy and his companions need to travel to different realms, including the Underworld, to figure out how to put the Earthshaker back to sleep. They encounter different gods and goddesses during their quest, and some might help while others might try to hinder them.
A cool plot could be a time - travel fanfiction. The Minotaur travels back in time to the era when the gods were more actively involved in the mortal world. He could interact with the gods, and Percy has to follow him through time to stop him from causing chaos. This would involve Percy having to deal with different rules and powers in the past, and also understanding the Minotaur's motives for going back in time.
One interesting plot could be where the NPU (assuming it's some new power or entity in the Percy Jackson universe) is a key to unlocking an ancient prophecy that no one knew existed. Percy and his friends have to figure out how to use the NPU to their advantage while also dealing with the usual monsters and gods trying to stop them.
One interesting plot could be the crossover of characters from 'Percy Jackson' and 'The Selection' universes. Maybe Percy finds himself in the world of 'The Selection' and has to deal with the different social and political structures there while still having his demigod powers.
One interesting plot could be Percy having to face an ancient, long - forgotten monster that wasn't in the original series. It adds a new level of danger and adventure.
One interesting plot could be Nico's journey to fully understand and control his powers in a new way that wasn't explored in the original books. Maybe he discovers a hidden aspect of his underworld powers that helps him save Percy from a new and powerful enemy. Another plot could involve Percy and Nico teaming up to explore a forgotten part of the mythological world, like a lost island full of ancient monsters and forgotten gods. It could be filled with action - packed battles and the discovery of new magical items.
Another plot might be a scenario where Percy tries to reason with Kronos. He could attempt to understand Kronos' motives for wanting to destroy the Olympians and find a compromise. This would be a complex and emotional journey as Percy has to face the being who nearly destroyed his world.
One interesting plot could be Percy having to face an alternate version of himself that has turned evil due to some dark magic. This would create a great internal conflict as he battles not only an external foe but also his own dark side.
Another possible storyline is a story focused on a half - wizard who is an outcast in both worlds. They don't quite fit in with the wizards because of their demigod side, and they're not fully accepted by the demigods either. This character then goes on a journey of self - discovery, trying to find their place in either world or create a new place for themselves where they can use both their wizard and demigod powers.