One idea could be Percy exploring his new powers related to Demeter. Maybe he can control plant growth in unique ways, like making plants form protective barriers. Another could be his interactions with Demeter's other children. He might face some jealousy from them at first but then prove himself and form strong bonds.
A possible plot idea is that Percy, as the adopted son of Demeter, gets involved in a conflict between Demeter and another god over the use of the land. The other god wants to use it for some destructive purpose, and Percy has to use his skills and the support of Demeter's followers to stop it. He might also have to deal with his own identity crisis as he is different from the typical demigods and struggles to find his true role in this situation.
One idea could be Percy having to work with Demeter to save a magical grove that's being poisoned. Demeter could be initially distrustful of Percy, but as they face challenges together, she realizes his worth.
Well, a cool plot might involve Percy being thrust into a situation where he has to mediate between Demeter and another god who has accidentally (or not) damaged one of her main domains. He could be championing Demeter's cause in a sort of divine court. Also, Percy could be involved in a story where he discovers an ancient prophecy related to Demeter that only he can fulfill as her champion, which leads him on a journey filled with mystery and danger.
One idea could be Percy having to deal with the stigma of being associated with Hades in the demigod world. He might face distrust from other demigods who are scared of Hades' reputation.
Well, a plot could involve Percy being sent on a special mission by the Fates. Since they control destiny, this mission might be crucial for the balance of the entire demigod world. He could have to face enemies that are normally out of reach for regular demigods. Along the way, he discovers secrets about his adoption that change his perspective on his life and his role among his peers.
One idea could be Percy having to learn the ways of Artemis's hunters. He might struggle with the no - male - contact rule at first but then find unique ways to bond with his new sisters. Another could be Percy going on a quest specifically related to Artemis's domain, like protecting a sacred forest. And he could use his water powers in new and unexpected ways in the context of Artemis - related tasks.
One idea could be Percy struggling with the dark influence of Kronos while still trying to maintain his loyalty to his friends at Camp Half - Blood. Another could be Percy having to hide his true identity as Kronos' adopted son from his closest allies. Maybe he discovers some long - lost powers or knowledge that Kronos had hidden away for him, which he must use to either save or destroy the world of the gods.
One idea could be Percy's struggle with his new identity as Nyx's adopted son. He might face discrimination from some of the other demigods who are suspicious of his new connection. Another plot could involve Percy learning new powers from Nyx that set him apart in battles against monsters. He could also have to deal with Nyx's enemies who target him because of his relation to her.
One idea could be Percy struggling to fit in with Athena's children at first. Since he's used to being a son of Poseidon, he has different ways of thinking and acting. Another plot could involve him using his newfound Athena - given wisdom to solve a really complex mystery in the demigod world. Maybe he discovers a new prophecy related to Athena that only he can understand because of his unique position as her adopted son.
One idea could be Percy having to learn the unique skills of Hephaestus' cabin, like forging magical weapons. He might struggle at first because he's used to his own powers. Another could be him having to deal with the other Hephaestus kids who are initially jealous of his fame as Percy Jackson but then come to accept him. And he could go on a quest where his new skills as an adopted son of Hephaestus are crucial in defeating a powerful monster.
Another plot idea is that Percy discovers secrets about his adoption. There could be a prophecy related to him being Thanatos' adopted son that he has to fulfill. This might involve him making difficult choices between his old life as a son of Poseidon and his new role, and he may have to find a way to combine the powers and responsibilities of both.