There's a possibility that a new, unknown and powerful monster could be the captor. This monster could be a hybrid of different mythological creatures, created by some dark magic. It has heard of Percy's fame and power and wants to keep him captive either to study him, or to use his power to become even more powerful itself. It could have a lair in a hidden and dangerous place, like an underground cavern filled with deadly traps.
Well, it depends on the specific fanfiction. Sometimes, Percy might get help from an unexpected source. He could befriend a magical creature that is also held captive by Luke and together they come up with an escape plan. He might also discover a hidden passage or weakness in Luke's lair that he can use to his advantage. Another possibility is that his friends from Camp Half - Blood somehow find out where he is and stage a rescue mission.
One plot idea could be that Percy is held captive by an ancient, forgotten sea deity who wants to use Percy's powers for its own dark purposes. Maybe this deity has the ability to manipulate water in ways that even Percy hasn't seen, and he has to find a way to outwit it using his wits and the limited power he can access while captive. Another idea is that he's held captive by a group of rogue demigods who believe Percy is a threat to their new world order. They try to brainwash him into joining their side.
It might be a powerful magical being. This being could be on a mission to study the Powerpuff Girls' powers and in the process of capturing Bubbles, realizes she has a very special personality. He is intrigued by her and as they interact more, love blossoms between them.
Well, sometimes in fanfiction, his brother might be a mortal who discovers his demigod heritage later. This could add an interesting twist to the story as he has to adapt to the world of gods and monsters. Or it could be a long - lost half - brother from a different camp, like a son of Poseidon from another part of the world who was hidden away for some reason.
She might be a character created to add a new twist to the story. For example, she could be a demigod with a very rare power that no one has seen before. Ariana could be a key to solving a big mystery in the fanfiction world. She could also be an antagonist at first, but then later become an ally to Percy after some character development.
He might meet some native Alaskan spirits. These spirits could be like the nature spirits he has encountered before but with their own unique Alaskan characteristics.
Well, in the 'Percy Jackson hunted by Shield' fanfiction, Percy's main source of help would be his demigod comrades. Annabeth Chase, with her brilliant mind and knowledge of architecture and strategy, could help Percy plan his escapes and defenses. Grover Underwood, being a satyr, has a connection with nature that could be used to create barriers or mislead Shield's agents. Additionally, Chiron, the centaur trainer at Camp Half - Blood, might have some ancient knowledge or magic that could be used to protect Percy or make him less detectable to Shield. There could also be other demigods with unique powers that could come to Percy's aid, for example, those with the power of invisibility or mind - control who could use their abilities to disrupt Shield's operations.
He could meet some Aboriginal heroes or spirits. They might have their own powers and knowledge that Percy can learn from.
Percy might encounter Baba Yaga. She is a well - known figure in Russian folklore. She could be an adversary, testing Percy's skills and his knowledge of the magical world. Or perhaps she could be a source of information if Percy manages to earn her respect. He could also meet the Rusalki, water nymphs from Russian mythology. Given Percy's connection to water, it would be interesting to see how he interacts with them.
Some minor gods related to the earth like Demeter could be allies. She has her own powers over the earth and could teach Percy some of her techniques. Also, the nymphs, such as the water nymphs and the tree nymphs, could be allies. The water nymphs could help with the water sources within the earth (like underground rivers) and the tree nymphs could help Percy take care of the forests. And let's not forget the pegasi. They could be used for transportation when Percy needs to quickly travel across his earthly domain.