Cynthia is the Champion of the Sinnoh region and hails from Celestic Town, where her grandmother, Professor Carolina, runs a Pokémon research lab. During her childhood, she received an egg that hatched into a Gible, which she trained and eventually evolved into her primary battling partner, Garchomp. In her early years as a trainer, Cynthia was solely focused on becoming stronger, which sometimes led to reckless behavior that caused her Pokémon distress. Her perspective changed significantly when she discovered the legends of the Sinnoh region's temporal and spatial Pokémon, leading her to adopt a more thoughtful approach to training. She eventually rose through the ranks to become the Sinnoh League Champion.

Cynthia is known for her calm, level-headed demeanor, even in the most intense battles, and is widely respected as a trainer who combines immense power with grace and precision. She frequently substitutes her Pokémon during battles to disrupt her opponent's momentum and gain strategic advantages. Beyond her battling career, she is also a dedicated archaeologist with a deep knowledge of Sinnoh's mythology and a growing interest in the legends of other regions. Cynthia strongly values the bond between trainers and their Pokémon, often quoting the ancient saying, When every life meets another life, something will be born. She has a mentoring nature and willingly offers advice to younger trainers such as Ash, Paul, and Iris to help them grow. Outside of training and research, she enjoys relaxing at her villa and has a well-known fondness for sweets, though she often struggles to choose which flavor to have.

In Pokémon Journeys: The Series, Cynthia is revealed to be a participant in the World Coronation Series, where she achieves a top-eight ranking in the Master Class and is seeded as the second-strongest trainer in the tournament behind the Champion of the Galar region. Her motivation for entering the competition appears to stem from a waning love for battling, as she eventually confides to another Champion that she intends to retire from competitive battling following the tournament. Throughout the series, she continues to research Sinnoh's history, often crossing paths with protagonists Ash and Goh during their investigations of legendary Pokémon. She also reunites with her longtime friend Dawn and former travel companion Brock to help thwart a revived Team Galactic plot, taking down three of the organization's commanders single-handedly.

Cynthia maintains several key relationships that highlight her role as both a goal and an ally. For many trainers, including Ash and his former rival Paul, defeating Cynthia has been a long-standing ambition since her first appearance in the Diamond and Pearl series. During the Masters Eight Tournament, she is reunited with Iris, the Unova Champion whom she has previously mentored and who specifically challenged her due to her affinity for Dragon-type Pokémon. Cynthia also shares a respectful, friendly rivalry with the Kalos Champion, Diantha, to whom she reveals her plans for retirement and ultimately discusses her renewed passion for battling. Her bond with Ash is particularly significant, as their semifinal match pushes her to her limits and causes her to reconsider her future. After being narrowly defeated by Ash's Lucario, Cynthia decides not to retire, realizing that she still has much more to learn, and she stays to watch Ash's final match against the Galar Champion.

Cynthia is widely regarded as one of the most powerful trainers in the world, and her abilities are consistently demonstrated throughout the series. Her signature Pokémon, Garchomp, is an exceptionally fast and hard-hitting dragon that she has raised since it was an egg. She commands a diverse and well-rounded team, including Spiritomb, Roserade, Milotic, Gastrodon, Togekiss, and Kommo-o, each of which is highly capable in battle. In the Masters Eight Tournament, she demonstrates her tactical versatility by employing different battle mechanics, including both Mega Evolution and the Galar region's Dynamax phenomenon, using the latter on her Togekiss in a strategic attempt to disrupt her opponent's rhythm. Her calm, analytical approach in battle allows her to adapt quickly to her opponent's strategies, and she is known for not showing stress even when surprised. Her defeat at Ash's hands is framed not as a failure, but as a moment of reinvigoration that transforms her original goal of retirement into a renewed commitment to mastering the art of Pokémon battling.