Jessie would be that really excited girl who's very energetic and is a tsundere, she can be that gangstery girl who has like a tragic past and bullies kids. She would have a pet Meowth that she would bring to school everyday in secret and is very affectionate to it. After she's done with homework she'd do her team rocket duties with her partner James and pet Meowth.
James would be that orphan who is a nerd as well, he could be a teen designer as he designed the outfits for team rocket. He could also be that kid that everyone calls gay since he crossdresses sometimes. He is very obedient, well mainly to Jessie and Meowth, he could be obsessed with gardening and always buy roses hoping someday he will have courage to give one to Jessie.
Meowth is that Pokémon that hides inside Jessie's bag for the day, he can eat her lunch sometimes but only when he's really hungry, when a student sees him he pretends he can't speak the human language though it's really hard to because he's so used to it. Sometimes he accidentally talks but only when he's mad, he'd usually say something mean to them or something.
Cassidy would be that popular girl that a lot of boys like, Butch likes her the most though. She would easily brag to everyone about her success in school and bully Jessie and James for having lower grades than her. Just like Jessie she's kinda a tsundere but she likes multiple boys but as no interest in Butch (since he's not hot) She sometimes gets annoyed with Butch and treats him like a slave or say mean things to get him to go away, but she fails every time.
Butch is that guy that follows his crush around everywhere, just like Sakura from Naruto. He'd be her slave and everything and would stay with her through hard times. They are secretly friends but Cassidy is embarrassed about it since he's not hot or popular. Sometimes when she's mean to him it hurts him a lot but he stays strong and is always by her side.