Maybe a plot where Percy discovers a hidden part of Camp Half - Blood that has been long forgotten. This could involve him unearthing ancient secrets and powers that change the dynamics of the camp. There could be new friendships and rivalries as a result. For example, he might find a group of demigods who were exiled there long ago and now they have a chance to be part of the main camp again.
One interesting plot could be Percy having to face a new and powerful monster that is immune to water, which is his usual strength. It creates a whole new level of challenge for him.
Another plot could be Percy getting sent on a quest to a different dimension. In this dimension, the rules of the demigod world are all twisted. He has to figure out how to get back while also dealing with the strange new threats there. It could be a place where the gods are powerless or have different forms, and Percy has to rely on his wits and the skills he has developed rather than just his god - given powers.
Percy himself is often a very popular character. His heroic deeds and his relatable personality make him a fan favorite. Fans love to read about his new adventures.
A great plot might involve Medusa having a change of heart. For example, instead of being purely evil, she could be forced into her actions by some greater power. Percy then discovers this and has to decide whether to still fight her or help her. In a fanfic, this could add a whole new layer of moral complexity to their relationship. It could also lead to an alliance between them against a common enemy, which would be very different from the traditional view of their encounter.
A great storyline could also be about a group of demigods from Camp Jupiter going on a quest to retrieve a lost Roman artifact that is said to have the power to protect the camp from a new and powerful enemy. Along the way, they face various obstacles and have to use their Roman - themed powers and knowledge to overcome them.
Maybe there's a prophecy at camp that some misinterpret to mean Percy will bring destruction. So, the campers, out of fear for their safety, betray Percy. They could lock him up or try to send him away, even though Percy has always been loyal to the camp. He then has to find a way to either clear his name or find a new place where he belongs.
One interesting plot is Percy being summoned by a time - traveling device. He is brought to a future where the Greek gods are forgotten and the world is in chaos due to the lack of their influence. Percy has to find a way to bring back the knowledge of the gods and restore order, all while dealing with the strange new technology and a society that has lost its moral compass.
One possible plot could be that in the fanfic, Jason is jealous of Percy's natural leadership skills. Percy always seems to know what to do in a crisis, and the other demigods look up to him. Jason, on the other hand, feels like he has to constantly prove himself. So, he starts trying to outdo Percy in every mission, which leads to some tense and exciting situations. For example, they might both be trying to solve a mystery at Camp Half - Blood, and Jason's jealousy causes him to take unnecessary risks just to show he's better than Percy.
Sometimes, the plot revolves around Percy and the members of his harem going on adventures together. They could be exploring new and mysterious places, and during these adventures, their relationships develop and they face challenges as a group. In some 'percy x harem fanfic', there are also plots where Percy has to deal with jealousy and rivalry among the harem members, which creates a lot of drama and interesting relationship dynamics.
One possible plot could be Percy's struggle for survival in a harsh and unforgiving environment. Maybe he has to find food and water while fending off dangerous creatures. Another plot could involve Percy trying to figure out who left him for dead and seeking revenge.
One idea could be Percy having to face a new type of monster that is native to the area around Camp Jupiter. For example, a giant mechanical beast left over from ancient Roman battles. Another could be Percy forming an unlikely alliance with a Roman demigod who initially dislikes him because he's from Camp Half - Blood. Maybe they have to work together to solve a mystery within the camp that threatens both camps.
One interesting plot could be Percy's internal struggle with his new identity as the child of Kronos. He might battle against the dark urges that come with his heritage while trying to stay true to his friends at Camp Half - Blood. Another plot could involve Percy facing off against the other demigods who see him as a threat due to his relation to Kronos.