Well, a cool plot for Percy Jackson Olympian god fanfiction could be Percy getting transported to an alternate dimension where the roles of the Olympian gods are completely reversed. The minor gods are in power and the major ones are in a subservient position. He then has to figure out how to get back to his own world while also dealing with this new power dynamic. Also, he could discover a hidden connection between his own powers and an ancient, lost Olympian god that was never mentioned before.
One idea could be Percy having to face a new, unknown threat that the Olympian gods are also powerless against. For example, a dark force from a long - forgotten realm. Another could be Percy going on a quest to find a lost artifact that has the power to reshape the relationship between the gods and demigods. Or perhaps Percy being forced to choose between loyalty to his friends and following the orders of the Olympian gods in a really tough situation.
In Percy Jackson Olympian god fanfiction, a great plot might involve Percy being framed for a crime he didn't commit by a jealous demigod who wants to take his place. The Olympian gods are divided on whether to believe Percy or not. As he tries to clear his name, he uncovers a conspiracy within the demigod community that is much larger than he thought. This could lead to him having to make some difficult choices about who he can trust among his fellow demigods and the gods themselves.
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.
Well, you could write a fanfiction where Percy loses his memory and has to rediscover his powers and his place among the demigods. Or perhaps a story about how the minor gods in the Percy Jackson universe form their own alliance because they feel overlooked by the Olympians. You could also create a fanfic that focuses on Annabeth's journey if she was separated from Percy and had to fend for herself in a dangerous situation.
In this kind of fanfiction, one possible plot could be Percy having to deal with the politics among the Olympian gods. He might try to bring about changes, like making the gods more involved in mortal affairs in a positive way. For example, he could convince them to be more proactive in protecting the environment which is being damaged by humans. Also, Percy would probably have to face new enemies. Since he's now an Olympian, he could attract the jealousy of some minor gods or ancient monsters who see him as a threat to the established order.
One idea could be Percy going on a quest to find a lost artifact that has the power to control the weather in the Olympian realm. This would put him in conflict with some of the gods who want to use it for their own purposes.
Perhaps in the fanfiction, the Elder Gods start to interfere with the modern world of demigods more directly. Percy and his friends notice strange phenomena, like the weather going haywire and magic behaving erratically. They soon find out it's because an Elder God is trying to regain its former power and is using the chaos to break through the barriers that keep it in a weakened state. Percy then has to find a way to stop it by using his unique connection to water and the help of his father, Poseidon.
One idea could be Percy having to face a new type of demon that is immune to water, his usual weapon. So he has to find a new way to fight. Another could be Percy being tricked into serving the God of Demons for a while and then realizing his mistake and trying to break free.
One idea could be exploring a new adventure where Percy has to team up with a minor god that has been forgotten. They could go on a quest to regain the forgotten god's power and status in the pantheon.
Perhaps Percy, as the God of Wisdom, has to deal with a situation where his wisdom is being questioned by the other gods. They don't believe that a former hero like him can handle the responsibilities of wisdom. So he has to prove himself by solving a complex problem that has been plaguing Olympus for centuries. He uses his unique perspective as a demigod - turned - god to come up with a solution that no one else could think of.
One idea could be Percy having to prove his divinity in a new way. Maybe he has to face a trial set by the gods where he can't use his usual powers but has to rely on his wits and faith. Another could be Percy interacting with a different pantheon's deities who mistake him for one of their own sons of god. He'd have to navigate their culture and rules.
Perhaps Percy, as the God of the Earth, has to plant the seeds of a new magical forest to restore balance to the world. But an evil force is trying to stop him by sending monsters to attack him and the forest he is trying to create. He has to use his earth powers to defend and also enlist the help of nature spirits like dryads. He also discovers that this new forest has a connection to an ancient prophecy that could change the fate of the world.