One potential new character could be a half - human, half - Titan who was hidden on Olympus. This character could have a complex backstory, being both feared and pitied by the gods. They could initially be an enemy to Percy, believing that Percy is just a puppet of the Olympians. But as the story progresses, they could become an ally, realizing that Percy has his own ideas and is not just blindly following the gods. Also, there could be a celestial being from a different realm who visits Olympus during Percy's time there and gets involved in his adventures.
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.
A new demigod from a really rare godly parentage, like a child of Hypnos, the god of sleep. This character could have unique powers related to dreams and illusions and could be an ally or an adversary to Percy. Another could be a centaur who has been exiled from his herd for some reason and has a vendetta against the Olympians. He could be a source of knowledge for Percy about some of the more hidden secrets of the gods.
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.
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.
Obviously, Percy would be one of the main characters. And probably the Olympian gods like Zeus, Poseidon, Athena etc. would also play important roles as he is raised in their domain.
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 could be a local guide in the place where Percy is exiled. This character could be an outcast from their own community and help Percy navigate the strange new land.
Obviously, Percy Jackson himself. Annabeth could also be there, as she is smart and would be interested in Percy's new - found fluency in Greek. Grover might tag along, adding his own unique perspective. And of course, Chiron, who has a deep knowledge of Greek culture and language, could play an important role.
There could be a chaos spirit named Eris. Eris could be a mischievous character who both helps and hinders Percy on his journey with chaos. She might have the ability to shape - shift into different forms related to chaos, like a swirling vortex of dark energy.
There could be a character who is a mentor to Percy in understanding his devilish side. This character might be an ancient being with knowledge of both the divine and the demonic. For example, a fallen angel who has seen the rise and fall of many with such mixed heritages.
There could be a time - keeper character. This person or being would be an expert in all things related to time and would either help or hinder Percy in his journey with his new power. Another new character could be a time - lost hero from the past that Percy accidentally brings forward in time.