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.
Obviously, Percy would be the main character as the story is about him getting sick. But his friends like Annabeth and Grover would also be important characters. They would be the ones trying to help Percy get better, so they play a big part in the fanfiction.
Grover could also be a main character. He might be at the scene when Percy gets drunk and try to use his nature - related powers to sober Percy up. Grover could also provide some comical relief with his reactions to Percy's drunken state, like his horrified expressions or his attempts to herd Percy like he would a wild animal.
Max's best friend could be a great supporting character. She could offer emotional support to Max during the pregnancy, give her advice on how to deal with Nathan, and be there for her when she's feeling scared or uncertain.
I think Hinata would be a great supporting character. Hinata is very empathetic and kind. She would be there to listen to Sakura's concerns and offer her quiet support. Also, Kakashi could play an interesting role. He might not fully understand what's going on but still offer his general wisdom and support to Sakura in his own unique, laid - back way.
Percy is surely a main character in this fanfiction. Depending on the universe it's set in, if it's related to a series like Percy Jackson, characters such as Annabeth, Grover, or his other demigod friends might also be important characters. They could either be the cause of Percy's anger or the ones who try to calm him down and help him through his angry state.
If Percy Jackson gets cancer in a fanfiction, it could completely change the nature of his adventures. His physical strength, which is crucial in the original stories, would be severely compromised. He might not be able to fight monsters as effectively. For example, he may struggle to hold his sword or run from danger. This could lead to new alliances, like relying more on his friends like Annabeth for physical protection while he uses his wits.
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.
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.
Another option is a group of anti - magic fanatics. They view Percy's wings as an abomination because they are a result of magic. They hunt Percy down, believing that by getting rid of him and his wings, they are protecting the world from the 'evils' of magic.