Nyarth, also known as Meowth, is a core member of Team Rocket alongside Jessie and James. Abandoned as a kitten at Camp Pokéhearst, he grew up scavenging for food on Hollywood streets within a gang of feral Meowth led by a Persian. His encounter with a female Meowth named Meowzie proved pivotal; her rejection drove him to teach himself human speech and bipedal locomotion to win her favor. This backfired when Meowzie deemed him unnatural, deepening his heartbreak. The first human word he understood, "rocket," inspired his choice to join Team Rocket.

Initially serving Giovanni directly, his ineptitude at basic tasks like serving beverages without spilling led to reassignment with Jessie and James. While occasionally claiming the title of Giovanni's "Top Cat," this was contradicted by Giovanni's actual Persian, which held the position and fueled Nyarth's envy and disdain for the species. His inability to perform the move Pay Day, a consequence of dedicating effort to human-like traits, further complicated his status.

He maintains a fierce rivalry with Ash's Pikachu, constantly scheming to capture it. Despite his antagonistic role, he shows unexpected loyalty to Jessie and James, cooperating with them during crises like escaping sinking ships or surviving natural disasters. He also exhibits empathy, particularly toward abandoned Pokémon, reflecting on his own past hardships.

Nyarth possesses a competitive streak against other Meowth. In Alola, he clashed with an Alolan Meowth that used flattery and cunning to temporarily win over Jessie and James, only to betray them later for a promotion within Team Rocket under Matori. In Hoenn, he developed a begrudging respect for Tyson's Meowth after witnessing its determination and battle prowess, including its victory against Ash's Pikachu at the Ever Grande Conference.

During the Pokémon Journeys arc, he continues devising capture strategies using Team Rocket's upgraded resources, like a capsule-dispensing machine providing random Pokémon and gadgets. Interactions with newer team additions, such as Morpeko consuming their food or Chewtle chewing Jessie's hair, add to his daily frustrations and adaptability. His role includes translating Pokémon speech and providing tactical support on missions across regions.

He consistently refuses evolution into Persian, viewing the species with contempt linked to his insecurities and past rivalries. His identity remains rooted in his unique traits—human speech, bipedal stance, and loyalty to his teammates—despite recurring failures in their pursuits.