Annabeth could be a major supporting character. She could use her wisdom to help Percy with the city's design, especially in terms of architecture and defense mechanisms.
There could be new characters as well. Maybe some local spirits or minor gods who are native to the land where Percy is building the city. They could offer their unique powers or knowledge to help with the construction, like a water nymph helping with the city's water supply system.
Grover could also be there. He might help Percy find suitable places for parks and nature reserves within the city, using his connection with nature. And he could be in charge of making sure the natural balance is maintained in the city.
It could be about Percy using his unique skills, perhaps his leadership and strategic thinking, to gather resources and a team to build the city. Maybe he faces challenges like natural disasters or lack of cooperation from some characters during the construction.
Annabeth could be a crucial supporting character. She might use her wisdom to come up with a battle plan. For example, she could figure out the best time and place for Percy to attack Gaea based on her knowledge of ancient prophecies and Gaea's patterns.
A wise old shaman from an Alaskan tribe might be a supporting character. The shaman could have deep knowledge of the spiritual side of Alaska and guide Percy in his training, perhaps helping him to connect with the forces of nature there.
There could be some minor gods or spirits as supporting characters. For instance, a nymph that lives near Percy's training area could provide him with fresh water or food when he needs it. A small god of the forest could give Percy advice on how to use the natural elements around him for his training. And there could be an old demigod who has retired from battles and now lives near Percy's training place. He shares his old war stories with Percy, which gives Percy new ideas and motivation for his training.
The other engines like James could be a supporting character. He could be a customer who is always very picky about his coffee. He might demand a very specific blend and keep coming back to check if they can make it better each time. Another could be Toby. He could be an old - fashioned customer who prefers simple black coffee and often shares stories from the old days with Thomas and Percy while sipping his coffee.
Annabeth could be a great supporting character. She might use her wisdom to help Percy figure out how to deal with the situation he's in after breaking something related to Hera. Grover could also be there, providing his unique perspective as a satyr and maybe using his nature - related powers to assist in any repairs or clean - up. Another possibility is Tyson, Percy's cyclops half - brother. His strength could come in handy when dealing with any physical challenges that arise from Percy's mistake.
Definitely his family members. His mother, for example, would be a crucial supporting character. She would be worried sick about him and would do everything in her power to take care of him. His father might also play a role, perhaps using his godly powers in some way to ease Percy's suffering.
Hermione could be a main character. She would use her intelligence and vast knowledge of magic to help Harry plan and build the city. Her skills in research and spell - casting would be invaluable.
Grover could also be a good support. His loyalty and friendship towards Percy could be enhanced in the context of Percy being the son of love. Grover could be someone who helps Percy reach out to other nature - loving demigods and spread love in that community.
A new character, like a chaos - born warrior with unique powers, could be introduced. This character could teach Percy about the ways of the Chaos realm and fight alongside him, becoming a close friend and ally in the process.