One possible plot could be Percy discovers he has a special connection to the Hellhounds. Maybe he is able to communicate with them in a way no one else can. He then has to use this ability to solve a mystery in the demigod world. For example, some important items have been stolen and the Hellhounds know where they are, but they will only tell Percy.
Well, perhaps Percy is made the King of Hellhounds by some ancient magic or prophecy. As the king, he has to lead the Hellhounds against a new threat that is emerging. This threat could be a powerful monster that is immune to normal demigod attacks, but the Hellhounds have a special way of dealing with it. So Percy has to train and organize the Hellhounds for battle.
A powerful Titan who wants to use the Hellhounds for his own evil purposes could be the main antagonist. He might try to capture Percy and force him to command the Hellhounds to do his bidding, like attacking the demigod camps.
One possible plot could be Percy Jackson having to navigate the complex politics of Rome as the King. He might face challenges from rival factions within the Roman demigod community who don't want an outsider like him in power. He could also be tasked with protecting Rome from new and powerful monsters that are specifically targeting the city because of his rule.
One possible plot could be Percy Jackson having to face new challenges after becoming the King of the Titans. Maybe he has to deal with the other gods who are jealous or afraid of his new power. He might also try to reform the Titan realm, making it less about domination and more about harmony.
Well, one possible plot could be Percy using his water - controlling abilities in the world of Alagaesia. Maybe he teams up with the local heroes there and they face some common enemy. For example, a powerful dragon that is threatening both the demigods' world and Alagaesia. He could also introduce new combat styles to the people of Alagaesia based on his training at Camp Half - Blood.
The plot might involve Percy's journey to becoming the king of the void. He could start by accidentally stumbling into the void. There, he discovers that there's a power struggle going on. With his friends' help, or maybe on his own, he has to prove himself worthy of being the king. He might have to face challenges like taming wild and otherworldly beasts, or solving ancient riddles that are the key to ruling the void.
Well, it could be about Percy using his demigod powers in the unique Alaskan setting. Maybe he has to deal with local mythological creatures that are specific to Alaska and assert his rule as the 'King of Alaska'. He might form alliances with native Alaskan demigods or spirits.
Well, perhaps in the fanfiction, Percy is summoned by the 'King under the Mountain' because of his reputation. The king wants Percy to retrieve a powerful and ancient artifact that was lost in a dangerous part of the mountain. Percy teams up with some of the king's bravest warriors. Along the way, they face all sorts of mythical creatures like trolls and goblins. Percy has to use his wits as well as his powers to overcome the obstacles and claim the artifact.
Well, it could be about Percy discovering he has the power to control wolves. Maybe he stumbles upon a hidden pack in the woods near Camp Half - Blood. The pack is in trouble, being hunted by some dark force. Percy decides to use his new - found ability to become their king and lead them to safety.
The plot might involve Percy Jackson as a king trying to make peace with Hera. Hera, who is often seen as a difficult goddess, could be causing trouble in the kingdom Percy rules. So, Percy has to use his wits and powers to handle her and the problems she brings, which might be related to a mysterious lemon - something, perhaps a lemon that has the power to either save or destroy his kingdom.
His friends from Camp Half - Blood would be his allies for sure. Annabeth, with her strategic mind, would be invaluable. Grover, the satyr, could help Percy communicate with nature spirits which could be useful. But also, some of the minor gods who feel left out by the major Olympians might side with Percy. For example, Hecate could use her magic to assist Percy, seeing him as a chance for a new order in the Olympian world. There's also Tyson, Percy's cyclops half - brother, who would be a strong and loyal ally.