Rio Kastle

Rio Kastle, known as Rio Kamishiro in the Japanese version, is a character appearing in the Yu-Gi-Oh! ZEXAL anime. She is the younger twin sister of Shark.

Appearance
Rio has dark pink eyes, and like her brother, she has pale skin and dark purple hair with light blue bangs. Rio also wears a ring on her right little finger, which was previously owned by her brother. Rio's appearance seems to attract many initial admirers, including Bronk.

Her attire includes a white jacket over a light purple shirt, black stockings and white shoes. The left coattail of her jacket has a conch-like ornament hanging down. At school, she wears the standard uniform, with her's being green due to her status as a second year student. She wears longer stockings than most female students.

Personality
Despite her appearance and previously spending a large amount of time in hospital, she is a confident and adamant person, getting annoyed when things do not go her way. This is usually shown when conversing with her brother. Her confident personality assists in her interests, allowing her to conquer sports such as soccer, baseball, basketball and boxing with ease. Despite all of this, Rio is extremely terrified of cats.

Rio tends to be annoyed when people refer to her as Shark's sister instead of calling her by her name, and especially does not like when someone insults her brother. This is further seen many times during her Duel against Aika as she got mad at her for making a rude remark about Reginald. She also snapped at Yuma for continually calling her "Shark's Sister". However, Yuma's usual antics makes Rio let it slide given that she is thankful to Yuma for helping her brother. It is also revealed that she goes very far on things and acts strong, because she feels she has to or people may use her as a shield against her brother. She later shows admiration towards Yuma and Alit as she commented they have amazing dueling spirit.

She takes great pride on her abilities and effort as has no problem in showing them when people understimate her as she believes women are not to be viewed as "pretty decorations".

Abilities
Rio has an unknown connection with the Barian World and its denizens. When Gilag arrived on Earth, it caused her great pain and she foretold that "they" were coming to take "the most important thing". When Misael arrived later, Rio went into a trance-like state and again said that someone was coming to destroy "the most important thing" and then describing a dragon of ill omen that would destroy everything. She once more senses the presence of Barian, and reports they are attacking Yuma.

When on those moments Rio enters some sort of trance while a mysterious red aura appears around her.

History
As children, Rio and her brother Reginald were visiting a theme park where she offered Reginald one of two rings which they both could wear. Reginald initially refused to wear it causing Rio to throw them on the ground and walk away in anger.

Rio once Dueled Quattro who was operating under the orders of Vetrix. He played a card, "Flaming Hell Blessing", that set the surrounding area on fire. She was critically injured in the blaze, though Quattro carried her to safety, his face being scarred in the process. After this, Reginald began wearing both of the rings from their childhood to remind himself of her.

In order to help his sister, Shark entered the National Duel Circuit and made it to the final match against Quattro. In the break room, Quattro set his Deck up to fall on the floor, causing Reginald to see some of its contents. This caused him to be disqualified.

Yu-Gi-Oh! ZEXAL II
Even after the World Duel Carnival, Rio was still in the hospital, albeit with only bandages covering her eyes. For some reason, Rio felt Gilag's arrival from the Barian World, which caused her pain. Because of this, Reginald (who by now often used "Shark" as a nickname) arrived later along with Yuma and Tori after him being called by the hospital as well as sensing Rio's pain. During that time Rio blurted out that someone is coming to take the most important thing, which worried Yuma as he had heard something similiar before.

Shark visited Rio at hospital again and gave her one of the rings from their childhood. She was later abducted by Chitaro Ariga, who was following Gilag's orders and was imprisoned in a cage within Sentaro's manga book. Sentaro approached Shark and informed him of this, causing them to Duel. When Shark attempted to use "Zeus Breath", Sentaro claimed that the manga world be destroyed if he lost - with Rio still inside it. Yuma and Rei Shingetsu went to Sentaro's manga writing room and managed to find several pages detailing how the Duel would go, as well as the result, which resulted in the death of both siblings. However, Shark called out to her and their bond managed to shatter her imprisonment, making her appear on top of a tower on the "Comic Field" Field Spell Card. When her bandages are blown off of her face, she insulted Shark's Dueling skills. After the Duel, she collapsed and was carried away by Shark.

After her recovery, Rio was able to return to Heartland Middle School. On her first day back, she intended to go with her brother, but he ran ahead without her. When she found him, she called him a jerk and told the gathered students he could never do anything without her. She ate lunch on the roof with her brother, Yuma and his friends. She speaks with Yuma, realizing he's the one who beat her brother earlier, but believed him to be Kite. When she found out who he really is, she recalled his catchphrase and then mispronounced it and is annoyed when Yuma refers to her as "Shark's sister". Their lunch is interrupted by a group of students representing various clubs, including Yata-Garasu. They wanted Rio to become their manager. She agreed to visit each club, but would only join if they defeated her in the club's activity. By herself, she defeats the school's soccer team and various other clubs, chiding them for asking her to manage them when they can't play. She said that she had to be strong, as she didn't want anyone to use her weakness to get to her brother. She is then approached by members of the Ikebana Club, who invite her to join them. When the arrive, they are introduced to Aika Hanazoe, the club's leader. The entire club had been hypnotized by Gilag and Aika put everyone to sleep. However, Yuma and Rio were both able to resist (and unbeknownst to either of them, Rei Shingetsu as well). Though she intended to Duel Yuma, Rio stepped in and challenged her instead. Despite her use of a "Chaos Xyz", Rio countered her moves and defeated her with "Sylphine, the Cold Bird Beast". Yuma then nearly called her "Shark's sister" again, but accidentally called her "Shark's brother" instead. Though initially annoyed, she eventually laughed and told Yuma that she had heard that her brother had changed a lot when she was in the hospital. However that he went back to the way he was because of Yuma. As the group walked home, Rio saw a cat and hid behind her brother, frightened.

Rio participated in the "Sports Duel Tournament" held by Yuma and his friends, where she ended up on a team with Bronk. They would be defeated by her brother and Yuma during the Volleyball Duel, but defeated Tori and Cathy in the Wrestling Duel. Afterwards, she complimented the two on their plays.

Sometime later, Rio went shopping with her brother. There, she sensed Misael's entrance to Earth and commented about a horrifying dragon. Knowing it to do with the Barians, they hurried to where Yuma was Dueling inside a Sphere Field generated by a Barian's Sphere Cube. Rio watched the rest of the Duel, which Kite eventually took over for Yuma. She looked on in horror when her brother attempted to save Yuma from his fall and ended up falling down the cliff himself. She visited her brother in the hospital while he was recovering.

One morning whilst talking to Tori at school, Rio sensed that Yuma was in danger, therefore she, Tori and Shark rushed to aide Yuma and Rei at the Heartland Pier where they entered a Battle Royal. After they managed to several several duelists, Gilag intervened, forcing all of the brainwashed students to attack Yuma, however Alit intercepted, using a combination of "Lightning Clinch" and "Brain Reboot" to defeat the remaining duelists. Rio then watched as Yuma began his duel with Alit in the Barian's Sphere Cube.

Reginald Kastle
Shark and Rio are twins and share a strong bond ever since they were children, symbolized by matching rings that Rio obtained. Following Rio's Duel with Quattro, in which she was critically injured and wound up in a hospital bed wrapped in bandages, Shark Dueled in the National Duel Circuit for her sake, but pressure was escalated to such an extent that he peeped at his opponent's Deck before the final match, an action that caused him to be disqualified and banned. During the time Rio was in the hospital to recover from her injuries, Shark often visited her.

Despite their bond, Shark has a typical tenuous "brother-sister" relationship with Rio, irritating one another and having normal siblings squabbles.

Deck
Rio plays an Ice Deck featuring WATER Winged Beast-Type monsters. Rio is also shown to be able to shift strategies easily, utilizing burn cards such as "Blizzard Falcon" and "Diamond Dust".