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.
Perhaps a plot twist where Percy discovers that his own powers are somehow linked to the Bane in a way he never expected. Like his ability to control water is actually being manipulated by the Bane to cause chaos in the ocean realm, which would put him in a really difficult position of having to figure out how to break that connection while still using his powers.
A possible new character could be an oracle - like figure who is not from the traditional Delphi but is a seer on Olympus. This character could give Percy cryptic prophecies that are related to the future of Olympus and the demigod world. There might also be a group of centaurs who are specifically trained to protect Percy and serve as his advisors, different from the ones at Camp Half - Blood.
Well, it depends on what you like. If you're a big fan of the Percy Jackson series, it might be interesting as it often takes the beloved characters and the world of Olympus in new and creative directions. Some fanfics in this vein are really well - written and add depth to the existing lore.
Perhaps in this fanfic, Percy is raised as a sort of prince on Olympus. He could be given tasks by the gods to prove his worthiness to be among them. This might include going on quests that are not just for the safety of the mortal world, but also for the stability of Olympus itself. He would also have to navigate the complex social hierarchies among the various gods and goddesses.
One unique aspect might be the way it reimagines the world of Olympus. If Percy is the Flame of Olympus, it might change the power dynamics among the gods and demigods. Maybe it explores how Percy's new status affects his relationships with his friends, like Annabeth, and his interactions with the various gods. Also, it could introduce new mythological elements or creatures that are related to this Flame concept.
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.
A new and powerful Titan who has been hiding and gathering strength all this time. He could be jealous of the Olympians' power and wants to take over. Percy would have to figure out his weaknesses and stop him before he causes too much destruction.
There could also be some ancient monsters or spirits that are tied to Olympus' existence. They might rise up to defend it because their own survival is linked to the continued existence of Olympus. These could be powerful beings that Percy has never faced before, adding an extra layer of danger to his quest to destroy Olympus.
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.
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.