A third potential character could be an ancient being known as the Keeper of Chaos. This being has been around since the beginning of time and holds the secrets of chaos. Percy has to seek this being out to understand more about his newfound love for chaos and how to control it without causing destruction.
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 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.
Perhaps some of the minor gods who are tired of the traditional power structure in Olympus could be Percy's allies. They might see his rebirth as a son of Chaos as an opportunity to shake things up. Also, any being that has a connection to the concept of change or new beginnings could potentially side with Percy. This includes spirits of innovation or even some forgotten heroes who sense that Percy is the key to a new era in the world of demigods and gods.
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.
There could be a new oracle who is specifically attuned to Percy's 'son of fate' situation. This oracle might be a young demigod with unique powers that help Percy understand his fate better. Maybe they can see visions of the future that are directly related to Percy's journey.
There could be a new bully at Goode who targets Percy because he senses Percy is different. This bully might turn out to have some connection to the mythological world, like being a descendant of a minor god.
There could be a healer character. Since Percy is a broken hero, someone with the power to heal his physical or emotional wounds might be introduced. This character could have their own backstory and motives, perhaps being related to an ancient Greek deity of healing in a new and unique way.
There might be new gods or minor deities introduced. They could be ones that have been forgotten or ones that are from a different part of the mythological world. Their appearance could change the power dynamics in the story. They might either help or hinder Percy in his second - chance journey.
Obviously, Percy Jackson is the main character. He is the one who becomes the soldier of chaos. His character development from a hero of the Olympians to a figure in the chaos realm would be a central focus.
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.