Jaime could also be a main character. His relationship with Cersei is complex and her weight gain might have a significant impact on their relationship. He might be involved in her journey, either as a support or as a source of conflict.
Tyrion could potentially be a main character as well. He has a long - standing feud with Cersei. Her weight gain might give him new ammunition to taunt her, or it could lead to a different kind of dynamic between them where he starts to see her in a new light, perhaps feeling a bit of pity or confusion about this change in her.
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.
A plotline might involve her relationships with other characters. For example, Jaime might have a different reaction to a heavier Cersei. He could be more protective or, on the contrary, feel a sense of distance due to the change. And her enemies might underestimate her because of her weight gain, only to be outwitted by her.
Obviously, Bowser would be one of the main characters as it's about his weight gain.
In 'college weight gain fanfic', the main characters are often college students. You'll find the jock type who, due to an injury or change in routine, starts to gain weight. There could also be the nerdy student who spends so much time studying and snacking that they start to put on pounds. And don't forget about the party - goer, who consumes a lot of alcohol and junk food at college parties, leading to weight gain.
I don't know since I don't have the details of the 'weight gain game story'. It could be a character named Bob who is trying to gain weight for a wrestling match in the game.
Obviously, Ash is the central character. Pikachu is also often included as Ash's closest companion. Misty and Brock might also be present. They could be the ones who first notice Ash's weight gain and either tease him or try to help him. Other trainers like Gary could also be in the story, perhaps competing with a now - heavier Ash and making snide remarks about his changed physique.
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.
Quinn Fabray could be involved too. Given her history of being concerned about her looks and status, a weight gain story for her could be about her learning to love herself regardless of the number on the scale. It could also involve her relationship with the other Glee club members as they support her through the process.
Well, obviously Tails is the main character as it's about his weight gain. But Sonic often shows up in these fanfictions too. Sonic might be there to support Tails, or he could be initially confused about what's happening to his friend. Another character could be Dr. Eggman. He might be the cause of Tails' weight gain, either intentionally through some evil plan or accidentally because one of his inventions backfires.
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.
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.