Percy himself is always interesting. In fanfiction related to The Staff of Olympus, he might have new challenges and growth. Another is Annabeth. Her intelligence could be used in unique ways to figure out the mysteries of the staff. Grover can also be really cool as he might use his nature - related powers in unexpected ways in relation to the staff.
One interesting plot twist could be that the Staff of Olympus has a hidden power that no one expected. For example, it might be able to reverse time in a small area, which changes the whole dynamic of a battle. Another could be that a character who was thought to be an enemy turns out to be a key ally in the quest related to the Staff. Maybe they were under a spell or had a secret mission all along.
Definitely Percy. His journey as a demigod, his encounters with various monsters and gods, and his growth throughout the series give a lot of material for fanfiction. Another interesting character is Nico di Angelo. His dark past, his powers related to the underworld, and his complex relationship with Percy can lead to some really engaging fanfiction stories. And we can't forget about Thalia. Her role as a daughter of Zeus and her leadership qualities make her a great character to explore in fanfiction.
Ares could be a likely character. He's always been somewhat of a wild card in the Percy Jackson series. He might betray Percy for his own amusement or to gain more influence in Olympus. Another could be Zeus. He's often paranoid about his power and might see Percy as a threat and betray him to protect his throne.
Percy Jackson and Annabeth Chase are definitely popular choices. Their relationship and their individual heroics are well - loved by fans. Another popular character is Nico di Angelo. His dark and mysterious nature makes for great fanfiction material.
Percy Jackson himself is always a popular choice. His adventures in the original series have made him a beloved character, and fans love to explore new scenarios for him, like what if he had different powers or faced different challenges.
Percy Jackson himself is likely one of the most important. He's the hero of the Percy Jackson series, and in this fanfic related to the Bane of Olympus, he would probably be at the center of the action, using his powers and wits to combat the threat.
There might also be some of the gods as main characters. For example, Poseidon, Percy's father. He could be involved in protecting Percy and guiding him in the new setting of Olympus, while also dealing with his own affairs among the other gods.
Percy himself is always a popular choice. You can explore his growth, his relationships, and his new adventures. Another is Annabeth. You could write about her architectural projects in relation to the Olympian world or her further adventures in wisdom - seeking.
Grover could also be a major character. As Percy's best friend, he would probably be involved in trying to stop Percy if he thinks Percy has gone too far. Or, if he sees the corruption in Olympus, he may side with Percy. Grover's connection to nature means he could play an important role in the events that unfold, like using nature spirits to either protect Olympus or aid Percy depending on his stance.
Obviously, Percy Jackson is the central character. But often, Annabeth Chase also plays an important role. She might come to visit Percy on Olympus and get involved in his adventures there. Also, the gods themselves, like Poseidon (Percy's father), Zeus, and Athena, are frequently main characters as they interact with Percy in the Olympian setting.