The main character is Percy, of course. But in addition to his close friends, some fanfictions might also involve the gods. For instance, Poseidon, Percy's father, could make an appearance. He might be worried about his son's condition and use his godly powers to try and save Percy. Or Chiron, the centaur trainer at Camp Half - Blood, would also be a key figure. He has a vast knowledge of demigod health and history, and would be guiding the others in their efforts to deal with Percy's collapse.
Obviously, the priestess herself is a main character. She is often depicted as having unique spiritual powers and a mysterious background. Naruto also frequently appears, as his story is intertwined with the events in the Naruto universe. Sakura could also be involved, perhaps as a friend or an ally to the priestess, using her medical skills to support the priestess in her quests.
Obviously, Tony Stark himself is the central character as it's about his collapse. But other key characters usually include Pepper Potts, his love interest. She often plays a role in either trying to prevent the collapse or dealing with the aftermath. For example, in some fanfictions, she's the one who discovers him first.
Percy is, of course, the main focus. However, in many of these fanfictions, Luke Castellan can also be a major character. Since Luke had his own issues with the gods and turned to the dark side in the original series, he could either be an influence on Percy's dark turn or an ally in his new dark journey. Nico di Angelo is another character who could be involved. Given his connection to the Underworld and his own complex relationship with Percy, he might try to understand what's going on with Percy or try to fight against him if he thinks Percy has gone too far.
There could be a mentor figure in the fanfiction. Maybe an old piano teacher who taught Percy everything he knows about playing the piano. This teacher could come back into Percy's life in the fanfiction to give him some crucial advice or to help him overcome a musical slump.
Another character that could be involved is Nico di Angelo. Since he has some experience with the Underworld and Tartarus, he might try to find a way to communicate with Percy or even attempt a rescue mission. His powers and knowledge would play an important role in any interaction with Percy in Tartarus.
Percy Jackson himself is obviously a main character. His struggle with bloodlust is often the central focus. Annabeth Chase also frequently appears as she tries to help Percy deal with his issues, using her intelligence and strategic thinking.
Obviously, Percy Jackson himself is often a main character. His ability to control water can be crucial when dealing with the effects of the Earthshaker, like tsunamis caused by the earthquakes. Annabeth Chase is also likely to be involved. Her strategic mind can help in planning how to approach the situation with the Earthshaker.
Percy Jackson himself is often involved. He might encounter the wolf in the woods around Camp Half - Blood and have to figure out if it's a friend or foe. Another common character is Annabeth. She could use her wisdom to analyze the significance of the wolf in the context of the Percy Jackson lore.
Percy Jackson himself is often the main character. He has a connection to the sea, and in pet fanfiction, he might find a sea - related pet like a hippocampus that he befriends and trains. Annabeth Chase could also be involved. She's smart and might use her knowledge to help with any problems the pet causes or gets into.
Obviously, Percy Jackson himself is often the central character in such fanfictions. His friends like Annabeth Chase can also be involved. In some cases, she might be the one trying to keep Percy out of trouble or, on the contrary, joining him in his 'delinquent' adventures. Grover could also be there, perhaps reluctantly getting dragged into Percy's misadventures.