There are two main characters here: Joho and Saphie. Joho is the one who falls ill, and his sickness will likely drive the plot forward as the story explores how he deals with it and tries to get better. Saphie, the one - eyed cat, is also a main character. Her one - eyed nature might imply that she has a different view of the world compared to other cats. In the fanfiction, she could be Joho's only hope for recovery, using her own mysterious cat ways to assist him.
The main characters are clearly Joho and Saphie. Joho is the one who gets sick, so he's likely to be at the center of the story's problem. And Saphie, the one - eyed cat, seems to be an important figure who will probably play a big role in dealing with Joho's sickness.
Maybe Joho's sickness could be a magical ailment that only Saphie, the one - eyed cat, can cure. For example, Saphie might have some special powers that are connected to her one eye, like the ability to see into the spirit world where the source of Joho's illness lies.
Another scenario could be that there is an antagonist in the story, someone who doesn't like Saphie because of her unique appearance. Jojo, being Saphie's friend, stands up to this antagonist. This results in Jojo getting hurt in the confrontation. The story could then focus on how Saphie tries to help Jojo recover and seek revenge on the one who hurt him.
It could be another animal in the neighborhood. Maybe there's a territorial cat that doesn't like Jojo and Saphie being around. This cat could attack Jojo when they cross into its territory.
Obviously Elsa herself would be one of the main characters since she is the one getting sick. Anna would also be a main character as she would be very concerned about Elsa's condition and would do everything she can to help. Olaf could also play an important role, using his cheerfulness to try to make Elsa feel better.
Obviously, Bendy would be one of the main characters since he's the one getting sick. His friends like Boris and Alice would also be main characters as they would likely be involved in taking care of him or finding a cure.
Mario would most likely be a main character too. He's Luigi's brother, so he'd be there to take care of him or at least be really worried about him. Princess Peach could also be a main character. She might visit Luigi when he's sick and bring some kind of magical item that could potentially help him get better.
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.
His friends like Batman and Nightwing could be main characters. Batman might use his detective skills to figure out what's wrong with Robin, and Nightwing could be there to offer emotional support.
Since Rigby is sick, his family members could also be main characters in the fanfiction. They might come to visit him and bring their own unique family drama to the story. And his friends from the park, like Muscle Man and High Five Ghost, could also be involved, trying to cheer him up while he's ill.
Sonic himself, of course. And his best friend Tails is very likely to be there. Tails is always by Sonic's side and would surely be there when Sonic is sick.