Citron is the Electric-type Gym Leader of Miare City in the Kalos region. His first encounter with Satoshi occurred after Satoshi was ejected from the Miare Gym; Citron intervened using his extendable mechanical arm invention to rescue him, initiating their travels together alongside Serena and his younger sister, Eureka.

Before this meeting, Citron had built an autonomous robot, Citroid, to manage the gym in his absence. However, an interruption during programming by Eureka caused an error, leading Citroid to reject Citron's authority and enforce overly strict battle conditions. This malfunction resulted in Citron and Eureka being expelled from their own gym, prompting Citron to capture a Bunnelby and develop countermeasures against his creation.

As an inventor, Citron frequently designs mechanical devices to solve problems encountered during travel. These inventions often malfunction or explode shortly after activation, becoming a recurring feature of his activities. His signature phrase when presenting a new device is "The future is now, thanks to science! Citronic Gear, On!" Examples include automated Pokémon trackers, language translators, wake-up machines for Eureka, and exercise equipment. Despite frequent failures, he persists in refining his inventions, viewing them as tools to assist humans and Pokémon.

Initially shy around strangers, Citron gradually became more confident and outgoing through his travels with Satoshi. He acts as Eureka's guardian in their mother's absence. Eureka frequently attempts to find potential romantic partners for him, leading to comedic situations where Citron uses his inventions to physically remove her from these interactions while expressing embarrassment. As Eureka is too young to be a Pokémon Trainer, Citron captures and officially registers Pokémon like Dedenne on her behalf, which she then cares for.

In battle, Citron relies on strategy alongside his Electric-type specialists like Magnemite, Magneton, and Heliolisk. His Bunnelby and later Chespin—received from Professor Sycamore—form core members of his active team. His battle style emphasizes tactical use of moves like Dig, Mud Shot, and Pin Missile over pure power. His growth as a Trainer is demonstrated when he confronts and defeats Citroid in a formal gym battle to reclaim his position, utilizing Bunnelby's type-disadvantaged resilience to overcome Heliolisk.

Later, during a return to Miare City for Satoshi's scheduled World Championships match against Elite Four member Drasna, Citron reunites with Satoshi and participates in intensive pre-battle training sessions focused on refining strategies and strengthening teamwork, highlighting their enduring friendship and his supportive role. He continues overseeing the gym when not traveling, maintaining dedication to both his duties and inventive pursuits.