One idea could be that Percy, raised by animals, has a unique understanding of nature and can communicate with them in a special way. This could lead to him using animals to gather information or as allies in battles against monsters. For example, birds could be his scouts, and larger animals like bears could be his bodyguards.
Well, perhaps Percy is raised by a group of monsters who are actually being controlled by an even more powerful and malevolent force. Percy then has to figure out how to break the control over the monsters that raised him and turn them into allies. He could start having strange dreams or visions that give him clues about his true heritage and his purpose in this situation. And as he grows up, he starts to notice differences between himself and the monsters, which makes him question everything he's been taught.
One plot idea could be Percy learning advanced combat skills from Chiron at a very young age. Since Chiron is a great teacher, Percy could become an even more formidable hero earlier. Another could be Percy having a closer bond with the centaur community because of Chiron. He might be involved in their internal affairs and help resolve conflicts among them.
One plot idea could be Percy having to team up with Hera to rescue a group of demigods who have been captured by an ancient monster. Hera, despite her usual aloofness, realizes she needs Percy's unique skills.
Perhaps Percy raised in Atlantis could be involved in a mystery related to the ancient history of Atlantis. There could be a hidden power or artifact that he has to find before the wrong people do. As he searches, he uncovers secrets about his own family that are tied to Atlantis. Along the way, he has to face challenges like underwater monsters that are specific to the Atlantean depths and overcome them using his wits and powers.
One idea could be that Percy has unique powers given to him by Chaos. For example, he might be able to control the very fabric of the universe in small ways. Maybe he can manipulate time on a very limited scale, like slowing it down during a fight to gain an advantage.
One idea could be that Percy is raised by Poseidon. He grows up with a deep understanding of the sea and its powers from an early age. This might lead to him having a more solitary childhood as he has to hide his connection to the god. Another plot could involve Percy being raised by Athena. He would then be extremely intelligent and strategic, perhaps getting into trouble at school for being too smart. A third idea is if he's raised by Apollo. He could have a natural talent for music and healing, and his adventures might revolve around using these gifts in a world that is both dangerous and full of mythical creatures.
A plot could be that Sally Jackson plants a lemon tree in her garden that turns out to be a gift from a minor goddess. The lemons from this tree have the power to give those who eat them the ability to see through illusions for a short time. Percy uses these lemons to his advantage when he is on a mission to retrieve a powerful artifact that is guarded by a monster that uses illusions to protect it.
Perhaps a fanfiction where Percy and Thalia are transported to an alternate dimension. In this new world, they have to figure out how to get back while also dealing with different versions of their friends and enemies. Thalia might have to face an alternate version of herself who has turned evil, and Percy could be the one to help her see the light again. It would be full of action, drama, and self - discovery.
A plot could involve Hera taking Percy on a journey through the past to show him the origins of the gods' power and how it relates to the current problems in the demigod world. This would give Percy a new perspective and knowledge that he can use to save the day. Or perhaps Percy accidentally stumbles upon a secret of Hera's that she's been hiding for centuries, and she has to enlist his help to keep it safe, all while other gods are trying to uncover it too.
Another plot idea could be that Percy discovers a hidden underwater civilization that is not related to Poseidon. This civilization has its own set of rules and powers. Percy has to navigate through their complex society and politics while also trying to convince them to help the demigods in a coming war against an ancient evil that is rising again. The underwater civilization could have unique magic and technology that the demigods have never seen before.