|“||The only reason the boss sent you to Hoenn in the first place was to get rid of you!||„|
|~ Cassidy to Jessie and James|
Cassidy's partner is Butch, and she is one of the few that usually manages to get his name right, much to his frustration as everyone else also calls him either "Biff", "Bill", "Bob", "Hutch", "Butcher", "Patch", "Botch", or "Buffy", among others (コサンジ Kosanji in Japanese).
Cassidy and Jessie met either before or shortly after their both joining Team Rocket, and are assumed to have been rivals since then. Unlike Jessie, Cassidy keeps her cool easier and is much less prone to violent outbursts. She also often referenced to Jessie, her awareness of Giovanni's dislike towards the Trio, and that they were likely to be thrown out of Team Rocket, something that Jessie usually ignores.
However, just like Jessie, Cassidy can be quite cowardly and bumbling in nature, as her and Butch's plans to steal Pokemon have failed miserably, which took a toll in her pride as she admits in an upsetting manner that it's so sad for their plans to end in such humiliation.
She first appeared in The Breeding Center Secret, where she and Butch build and advertise a fake breeding center to steal Pokemon. To further their goals, they framed Ash and his friends, as well as Jessie, James and Meowth, resulting them to be arrested. However Misty, Pikachu, and Psyduck gather enough evidence to prove her friends' innocence, resulting both Cassidy and Butch to be arrested while Jessie, James and Meowth escape from prison.
Cassidy returned again Pikachu Revolts, where she and Butch were bailed out by Giovanni and started a new plot to steal more Pokemon at Mandarin Island by using a Drowzee to turn all of the island's Pokemon against their trainers. However, they made a mistake in turning Jessie and James' Pokemon against their trainers, resulting an angry Jessie and James to briefly team up with Ash and his friends. Jessie, James, and Ash enter into a battle against Cassidy and Butch, which ended when Misty's Togepi uses Metronome to defeat Drowzee, resulting all the Pokemon to be free from Drowzee's control and Cassidy and Butch to be thrown back into jail, much to their dismay.
Cassidy appears in the Lugia story arc, where she and Butch teamed up with Dr. Namba to capture Lugia and its child. However, both Cassidy and Butch end up having a battle against Jessie and James (who attempt to beat them to it), but their battle frees Lugia, who then blasts both duos and their Pokemon into the sky.
Cassidy returns as a recurring antagonist in Pokemon Chronicles, where she and Butch try to steal Pokemon for Dr. Namba's new secret project. Similar to Jessie, James and Meowth in the anime, Cassidy and Butch serve as comic relief in the spinoff series, as they failed every time to steal Pokemon and get blasted off in the end, much to their complete embarrassment and distraught.