Poison Ivy could also play the role. She might use her plant - based powers to somehow influence Catwoman's diet or metabolism, causing the weight gain, and then use it as a way to manipulate her or get her out of the way in their shared battles for environmental causes in Gotham.
The Penguin could be a great antagonist. He might mock Catwoman for her weight gain, using it to try and undermine her confidence and take over her territory in Gotham.
The main antagonist could be a powerful sorcerer. As I mentioned before, in the context of a magical curse causing the weight gain. This sorcerer could have his own motives, like trying to take over the world by first weakening the Avengers' most iconic figure. He could use his dark magic to mess with Captain America's body and make him gain weight, and then use this as a distraction while he executes the rest of his evil plan.
Ra's al Ghul could also serve as the main antagonist. He might have a new plan for Gotham that involves using Catwoman as a pawn. He could be aware of her relationship with Batman and try to use it to his advantage. Batman would have to not only save Gotham but also rescue Catwoman from Ra's al Ghul's clutches.
Obviously, Bowser would be one of the main characters as it's about his weight gain.
It could be that Catwoman indulges in too much of Gotham's rich food while on a long - term undercover mission. This weight gain makes her more relatable to the common people she is trying to protect, and she uses her new look to her advantage in unexpected ways.
Well, Cersei herself is obviously a main character. Since it's a fanfic about her weight gain, the story would revolve around her experiences, emotions, and how she deals with this change.
It could be Chewbacca. Imagine Chewie getting stuck on a planet with limited food options that are all high - calorie. He might start to gain weight as he tries to survive on whatever he can find. And his weight gain could affect his ability to move around quickly, which is usually one of his advantages.
A young girl from a poorer district might be the main character. If there was some sort of relief effort where the Capitol sent a large amount of food to her district, she could be one of the first to gain weight. This would make her stand out in her district, and she might face both envy from those who are still starving and criticism from those who believe in the traditional, more slender body type of her district.
Perhaps an older, veteran hunter. After years of successful hunts, they start to relax a bit. They become less strict with their diet and start to gain weight. This weight gain makes them re - evaluate their hunting skills and they have to find new ways to be effective in the field again.
Obviously, Star Fox himself could be the main character. Since it's a 'Star Fox weight gain story', he would be the one experiencing the weight gain.
Homer could be involved. Since Homer loves food himself, he might either encourage Bart's new eating habits that lead to weight gain, or he could be the one trying to help Bart get back in shape. Marge would also be a key character. She would likely be concerned about Bart's weight gain and try to get him to eat healthier, constantly nagging him to stop eating junk. Lisa could also play a role. She might be initially teasing Bart about his weight gain but then feel bad and try to find a scientific way to help him lose the extra pounds.