The main character is Angelica. Then there are her parents, who play a crucial role in grounding her. Additionally, Susie could be a character in this fanfiction. She might be the 'good girl' contrast to Angelica. When Angelica is grounded, Susie could be having a great time with the other kids, which would make Angelica even more jealous and regretful of her actions that got her grounded.
In the fanfiction, Angelica could get grounded for lying to her parents. For example, she tells them she's going to a friend's house but actually goes to the park instead. Her parents find out and ground her. This would lead to her having to stay at home while the other kids are having fun outside, which could be a source of conflict and growth for her character.
Obviously, Seto himself would be the main character. He is the one who is getting grounded, so the whole story would revolve around him. His family members could also be important characters. For example, his parents or guardians who are the ones grounding him. They would play a role in setting the rules and enforcing the grounding. His friends might also be characters in the story. They could come to visit him while he is grounded or try to convince his guardians to let him go early.
Well, of course, Caillou himself is the central character. His parents also play important roles as they are the ones who ground him and teach him lessons.
Dumbledore can also be a significant character. He might be the one who decides Harry's punishment or he could be the one to offer some wisdom to Harry during his time of being grounded. And of course, the teachers like Snape or McGonagall could be involved as they are often the ones who enforce the rules and punishments at Hogwarts.
Obviously, Harry Potter himself is the central character. His friends like Ron Weasley and Hermione Granger are also often involved. They might try to visit him while he's grounded or come up with plans to get him out of being grounded. Dumbledore could also play a role, either as the one who enforces the grounding in some cases or as the one who might offer some wisdom to Harry during his time of confinement.
The Rugrats' Angelica is a complex character. In the show, she's often a bit of a brat. The real story behind her is that she's a typical spoiled only child in some ways. She likes to boss around the younger babies, Tommy and the gang. She also has an overactive imagination which often gets her into trouble or makes her believe she's in more important situations than she really is.
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.
The main characters in Rugrats Story are Tommy, Chuckie, Phil, Lil, and Angelica.