Kastle River

Despite her appearance and before spending a significant amount of time in the hospital, she is a confident and determined person, easily angered when things don't go her way. This is usually evident when she talks to her brother. Her confident personality serves her well in her pursuits, allowing her to excel in sports like soccer, baseball, basketball, and boxing with ease. Despite all this, Rio has a terrible fear of cats. Rio tends to get annoyed when people refer to her as Shark's sister instead of using her name, and she especially dislikes it when someone insults her brother. This is seen many times during her Duel against Lotus Hanazoe, when she became angry with her for making a rude comment about Reginald; even Yuma and Astral were startled to see her angry. She also reprimanded Yuma for constantly calling her "Shark's sister." However, Yuma's usual antics often cause Rio to let it go, as she is grateful to Yuma for helping her brother. It's also revealed that she goes to extremes and acts tough because she feels she has to be strong, or people might use her as a shield against her brother. Later, she shows admiration for Yuma and Alito, commenting that they have an incredible dueling spirit. She's very proud of her abilities and has no problem demonstrating them when people underestimate her because she believes women shouldn't be seen as just a "pretty face." Rio also has an empathetic side to her personality. This is shown when she sees Bronk injured on the way to school and shows genuine concern for him, helping him treat his wounds.

Rio has dark pink eyes, and like her brother, she has pale skin and dark purple hair with blue bangs. Rio also wears a ring on her right pinky finger, which belonged to her brother. Rio's beauty seems to attract many admirers initially, including Bronk. Her outfit includes a white jacket over a light purple shirt, black stockings, and white shoes. The left hem of her jacket has a shell-like ornament hanging from it. At school, she wears the standard uniform, which is green in her case due to her status as a sophomore. She wears longer black stockings than most of the students. Rio's outfit in her past life was that of a princess. She wore a long hood over her head, white sandals, a white dress, and three gold rings on her legs. She also wore this outfit when she was possessed by Abyss.

Rio has an unknown connection to the Barian World and its inhabitants. When Girag arrived on Earth, it caused her great pain, and she predicted that "they" had come to take "what is most important." When Mizar arrived later, Rio entered a trance-like state and again said that someone would come to destroy "what is most important," describing an ominous dragon that would destroy everything. On another occasion, she senses the presence of the Barians when Girag and a group of controlled Duelists are attacking Yuma. During these moments, Rio enters a kind of trance, while a mysterious red aura appears around her. After boarding the airship, Rio is able to see Astral. She expresses her joy when she can still see him even after leaving the airship.

It's based on a card duel that includes magic, traps, and monsters, where sometimes the owners gamble for fun. But in other dark circumstances, your life could be at stake.