One interesting plot could be a rap battle between Percy and Luke to decide the fate of Camp Half - Blood. Percy could rap about his loyalty to the camp and his friends, while Luke could rap about his disillusionment with the gods and his desire for a new order.
Percy could be a strong contender too. He has a lot of charisma and can be very persuasive. His experiences with the gods and his adventures would give him plenty of material for his raps. He could use his connection to the sea to create some really powerful and unique lyrics that would wow the crowd.
One possible plot twist could be that Percy discovers a hidden power within himself during the battle. Maybe he realizes he can control not just water, but also the heat from the hot springs in Thermopylae, using it to his advantage against the enemies. This new power could turn the tide of the battle in an unexpected way.
One interesting plot twist could be that a minor character from the original series turns out to be a powerful ally in the Battle of Manhattan in the fanfiction. For example, a seemingly harmless janitor at Camp Half - Blood who actually has the power to manipulate time and uses it to freeze the enemy forces at a crucial moment.
Maybe in the fanfiction, the zoo is a place where the gods have hidden some of their lost magical artifacts. Percy, being the son of Poseidon, senses a strange water - based magic near the aquarium section. He starts to investigate with Annabeth. Along the way, they face challenges from zoo security (who are unknowingly being influenced by a minor god who doesn't want the artifacts found) and various magical traps set around the exhibits.
A plot could involve Percy being sent to Forks on a quest. He discovers that there's a powerful artifact hidden in the area that could cause chaos if it falls into the wrong hands. The vampires and werewolves in Forks are also after this artifact for their own reasons. Percy has to navigate the complex relationships between these two groups while also trying to keep his true identity as a demigod a secret. Along the way, he forms an unlikely friendship with Jacob, who helps him understand the ways of the werewolves.
One possible plot could be Percy arriving in the DxD world and being mistaken for a new, extremely powerful devil. He then has to navigate the complex politics of the devils while also trying to find a way back home. Along the way, he uses his demigod powers in unique ways against the various threats in the DxD universe.
One possible plot could be that the Volturi from Twilight discover the existence of demigods from the Percy Jackson world. They see the demigods as a threat to their vampire supremacy. Percy and his friends have to team up with some of the more friendly vampires, like the Cullens, to fend off the Volturi. This would bring together the magic and powers of both universes in an epic battle.
Well, perhaps there's a villain in the Percy Jackson universe who discovers that the iCarly web show has a huge following and decides to use it as a way to spread chaos. The demigods have to team up with the iCarly crew to stop this. The iCarly gang has to learn about the world of Greek mythology really fast and help the demigods navigate the modern world of technology and media to defeat the villain.
Maybe Percy is on a quest and stumbles upon a group of magical creatures playing poker. They invite him to join. Percy, being Percy, is a bit clumsy at first but then realizes that the game has a deeper meaning related to the prophecy he is part of. He starts using his battle - trained mind to analyze the opponents' moves and the patterns of the cards, all while trying not to reveal his true identity as a demigod.
Well, it could start with a magical accident. In the Percy Jackson universe, a spell gone wrong sends Percy, Annabeth, and Grover into the land of Alagaƫsia from Eragon. There, they discover that the demigod powers Percy has are seen as a strange and new form of magic. Eragon is initially suspicious of them but realizes they can help in his fight against Galbatorix. They combine their skills, Percy's water - controlling powers and sword - fighting skills, along with Annabeth's strategic mind and Grover's nature - sensing abilities, with Eragon's dragon - riding and magic - wielding skills to take on the dark forces.