Percy is the central character for sure. In addition to his close friends, there could be some antagonist characters. For example, if Percy breaks his ribs because of an attack by an enemy, that enemy could be a main character too. They could be trying to finish Percy off while he's injured. And there might be some minor characters like other campers who also play a role in his recovery, either by bringing supplies or just offering moral support.
Obviously, Percy would be one of the main characters. His friends like Annabeth and Grover would also be important. They would be the ones to support Percy through his injury and help him recover. Maybe there would be some new characters introduced as healers or other allies who help Percy during this tough time.
Maybe some of the gods or goddesses play important roles. For example, Apollo, the god of medicine, could make an appearance. He might offer some magical healing or at least some advice on how Percy can recover more quickly. This would add an interesting mythological element to the fanfiction.
The plot could involve Percy having an accident during a battle. Maybe he's fighting a powerful monster and gets thrown against a hard surface, resulting in broken ribs. His friends then have to figure out how to get him medical help in the middle of their adventure.
Obviously, Bart would be one of the main characters since he's the one who breaks his arm. His family members like Homer, Marge, and Lisa are likely to be main characters too as they would be involved in his care and recovery.
Annabeth could be one of the main characters interacting with him. She might tease him about taking his shirt off, or she could be concerned if he's taking it off because of an injury. Their relationship is complex, and this situation could add a new layer to it.
The other members of the Bat - family like Robin, Nightwing, and Batgirl are likely to be main characters too. They would be involved in filling the void left by Batman in protecting Gotham.
Percy could be a fan of the original work that the fanfiction is based on. Maybe he's someone who has a deep understanding of the source material and thus is in a good position to break down the fanfiction.
He would surely interact with Annabeth. Their relationship is central in the Percy Jackson series, so in a Tartarus fanfic, she'd likely be there to support him or be in a similar situation as him.
Obviously, Luke and Percy are the main characters. Luke is the one doing the beating, and Percy is the victim in this scenario.
Percy Jackson himself would likely be one of the main characters. Also, Annabeth Chase as she is always by Percy's side. Grover would probably be there too since he's Percy's best friend.
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.