Jessica, known as Jessie and also by the Japanese name Musashi, is a key member of Team Rocket, operating alongside James and Meowth. Her core mission involves stealing rare or powerful Pokémon, especially Ash Ketchum's Pikachu, to further Team Rocket's aims under Giovanni.

Jessie's early life was unstable. Her mother, Miyamoto, a high-ranking Team Rocket agent, vanished during a mission to record Mew in the Andes Mountains, leaving Jessie in a financially struggling foster home. Food scarcity led her to occasionally eat snow, later recalled as "snowgasboard" meals. She nursed a childhood crush on Astin but declined his invitation to become a Pokémon Coordinator to pursue pop idol dreams with friends. Her failed audition crushed that aspiration while her friends succeeded.

She later attended Pokémon Nurse School, befriending a Chansey but failing to graduate due to her inability to perform moves like Sing. The Chansey gifted her half of its egg-shaped graduation pendant upon her departure. Jessie then enrolled at Pokémon Tech alongside James, both achieving the lowest scores in the school's history. They joined a Sunnytown bicycle gang, where Jessie earned the nicknames "Big Jess" and "Chainer Jessie" for brandishing chains while riding. Before Team Rocket, she held various jobs including modeling, weather reporting, and ninja training.

Jessie joined Team Rocket separately from James. During training, she fostered a fierce rivalry with fellow agent Cassidy and cycled through partners before permanent assignment with James and Meowth. Their first major mission targeted Pokémon at Viridian City's Pokémon Center, where they witnessed Ash's Pikachu's power and vowed its capture.

Jessie exhibits a volatile, vain personality, frequently enraged by insults to her looks or damage to her signature magenta hair. She favors snake-like and Poison-type Pokémon, like her former Ekans (evolved into Arbok) and Seviper, yet also adores cute Pokémon such as Smoochum. Despite her temper, she shows genuine care for her Pokémon: releasing Arbok to protect wild Ekans from poachers and freeing Dustox for a romantic pursuit with a shiny counterpart. Her loyalty extends to the accidentally obtained Wobbuffet, a steadfast companion despite comical interruptions.

Across regions, Jessie pursued Pokémon Contests and Showcases under aliases like "Jessilina" (in orange dresses and glasses) and "Jessilie" (in elaborate gowns). Initially unsuccessful, she won several Sinnoh ribbons using Dustox and Yanmega, reaching the Grand Festival Top 4. In Alola, she caught Mimikyu, which harbored intense hatred for Pikachu and often disobeyed commands to attack it. Their bond strengthened after Jessie repaired its disguise, though Mimikyu remained in Alola when the trio left.

In *Pokémon Journeys: The Series*, Jessie mentors a Ditto struggling with performance anxiety during filming. She helps it overcome fear by teaching it to "slap its own face" for focus, revealing unexpected empathy and echoing her own acting aspirations. Though Ditto returned to its career, Jessie wished it success from afar. Her tactical role involves devising schemes, like teleportation illusions using Ditto's transformations, though Ash persistently thwarts them.

Temporary promotions followed falsely claimed victories over groups like Team Galactic, but demotions resulted from repeated failures. Her perseverance endures despite Giovanni's frequent disapproval. Jessie's foundational relationship with James and Meowth balances her aggression with James's compliance and Meowth's translations, forming a resilient, comically flawed unit.