Rio Kazama is a professional wrestler training at Berserk Gym with four years of experience. She has short white hair, brown eyes, and a darker skin tone. Her wrestling attire in the anime features a purple two-piece outfit with black gloves, kneepads, and purple boots, while the manga depicts it as steel-blue with tight shorts. She also wears Berserk's standard gear: a white jacket with red sleeves and collar plus red track pants. Her entrance includes a hunter-themed mask and cape, accompanied by her signature phrase, "Now, it's hunting time!"

Initially, Rio displays a serious, aggressive, and impatient personality, showing little tolerance for those who disrespect professional wrestling. She humiliates Elena Miyazawa after hearing her dismiss wrestling as easy. This extends to her early interactions with Sakura Hagiwara, whom she defeats in a "Cabellera contra Cabellera" match, forcing a traumatic haircut on Sakura. Rio employs psychologically demeaning tactics like the "Shame Hold" to dominate opponents. After losing her rematch against Sakura, Rio demonstrates respect and sportsmanship by shaking hands and acknowledging Sakura's growth. She evolves into a supportive mentor, assisting Sakura in preparing for matches like the one against Blue Panther and expressing genuine concern for Sakura's career. Despite retaining her blunt demeanor, Rio develops camaraderie with Berserk teammates and shows protectiveness, notably objecting to the idea of Sakura retiring.

As a wrestler, Rio is an all-rounder proficient in throws, submission holds, and aerial techniques. Her signature moves include the sleeper hold (particularly the body scissor variation), joint locks, and the Northern Lights Bomb. She possesses notable physical strength, exemplified by lifting opponents with one arm or spinning them in chokeholds. Ranked 65th in the Shangri-La World Rankings, she is recognized as one of Berserk's top competitors.

Rio joined Berserk four years prior to the series after being inspired by the legendary wrestler Jackal Tojo. Her early career focused on climbing Berserk's ranks through rigorous training. Her pivotal role begins when she confronts Elena and Sakura during a television special, leading to the hair-match wager with Sakura. Though initially dismissive of Sakura's potential, Rio later softens during Sakura's initiation test at Berserk, subtly easing the final throw to help her pass. After her loss to Sakura in their rematch, Rio shifts from antagonist to respected rival, supporting Sakura during high-stakes matches like the bout against Jackal Tojo and the Blue Panther feud. In the OVAs, she participates in events like the hot water test and casually interacts with other characters.

Rio admires Jackal Tojo as her idol-turned-wrestling inspiration; transitions from antagonism to mutual respect with Sakura; and sustains friction with Elena due to differing attitudes toward wrestling. She also guides newcomers like Moe Fukuoka with characteristic sternness. Her design differs between manga (more beast-like) and anime (softer features), and she is inspired by real-life wrestler Mayumi Ozaki. Her catchphrase "You idol wannabes!" references wrestling lore.