Maybe Percy discovers a hidden garden and becomes obsessed with it. He starts to learn about different plants, takes care of them, and the garden becomes his special place.
There could be an old gardener who mentors Percy. The gardener might teach Percy all about the plants in the garden, their needs, and how to keep the garden thriving.
Another idea is that Percy discovers he has a long - lost vampire heritage. As he becomes a vampire, he starts to unlock memories and powers related to his vampire lineage. He could go on a journey to find out more about his vampire ancestors and the secrets they held, all while adjusting to his new vampiric existence which is full of both challenges and newfound abilities.
In this fanfic, Percy might be seen as an outcast at first among the Avengers because he's so different. But as time goes on, they come to respect his abilities. The story could also explore how Percy's presence affects the dynamics within the Avengers. Does he create new rivalries or alliances? And how does he adapt to their high - tech world when he's used to the more ancient and magical world of the Greek gods? Maybe he even tries to introduce some of his own magic into their technology, leading to some interesting and unexpected results.
Perhaps Percy is pushed to his limits by some great injustice in the story world. Maybe he witnesses the death of someone he loves at the hands of an evil force. This trauma could transform his personality, leading him to become a killer with a vendetta. He might start by targeting the ones directly responsible and then expand his scope as his thirst for vengeance grows.
Well, perhaps Percy discovers some ancient power within himself that gradually transforms him into a god. He might have to face a series of trials to fully ascend, like battling powerful monsters or making difficult moral choices.
If Percy Jackson becomes mortal in fanfic, he would likely lose his demigod powers. He might struggle to adapt to a normal human life. For example, he would no longer be able to control water or have his superhuman strength. He could face challenges like getting sick more often or not being able to defeat monsters as easily. His relationships might also change. His friends from Camp Half - Blood might have to protect him instead of fighting side by side with him.
Maybe Percy has been through a great betrayal, like his closest friend turned on him for power. So he starts to close off his emotions to avoid being hurt again.
It could be an ancient and powerful god who has long been plotting against Percy. This god might be jealous of Percy's power and popularity, so he devises a plan to turn Percy into a killer, knowing that it will lead to Percy's downfall and his own rise in power.
Obviously Percy himself. Also, Annabeth would probably be there as his girlfriend. Grover, his satyr friend, might also make an appearance. And the gods, like Poseidon, Percy's father, would surely play a role, either guiding Percy or testing him on his path to godhood.