Rio Kastle is an antagonist in Yu-Gi-Oh! ZEXAL. She is the younger sister of Reginald Kastle and a student of Heartland Academy. Later, on she is revealed to be Marin, one of the Seven Barian Emperors.
She was voiced by Alyson Leigh Rosenfeld.
Rio Kastle was known as Marin in her past life, she was a priestess as well as a princess of the United Lands of the Poseidon Ocean alongside her brother Nash. One fateful day their kingdom was attacked by a ruthless prince known as Vector, who led a army of soldiers to plunder the castle by using Gorgonic Guardians which in turn failed. and then Vector killed one his men and used him as a sacrifice to summon Abyss turning things in his favor, and Marin decided to offer her soul to Abyss and sacrifice herself then plunged herself into the depths of the ocean and summoned Number 94: Crystalzero to purify Abyss which was due to the Barian deity Don Thousand Influencing her and was later revived as one of the Seven Barian Emperors.
At another time, Rio and Reginald visited a theme park where the former offered the latter one of Kastle twins' two rings which they both could wear. Reginald initially refused to wear his ring, causing Rio to throw them on the ground and walk away in anger. In her duel with IV, she was involved into an incident and being hospitalized.
Powers and Abilities
Even before realizing her past as a Barian, Rio's athletic ability was anomalous and enabled her to defeat various teams in a gauntlet of sports and games, despite doing so in her standard school uniform.
With the use of Barian crystals or under the atmosphere of Barian World, Rio can assume the form of Marin, her Barian identity. The transformation allows her to access all of her otherworldly abilities; notably, her immunity to the corruptive influence of Number cards. This allows her unfettered control over her ace monsters: "Number 103: Ragnazero" and its upgraded form "Number C103: Ragnafinity".
In addition to that, she gains access to a technique called "Chaos Draw," the Barian equivalent of "Shining Draw." By channeling Chaos and Ener-D into her next draw, Marin can blindly shift the cards in her deck so that the one she desires ends up on top as she draws it.
Sensing of Barians' presence
Due to Rio's strong dedication to Barian World, her powers as Marin developed empathically, granting her minor abilites that other Barians didn't possess, even at full power. Rio can sense the presence of other Barians; even if said Barians are assuming human form, she can still sense them. This is in contrast to Girag and Alito, who couldn't sense when a Barian like Vector is right in front of them.
Unbeknownst to her, Bronk has secretly fallen in love with her and they became very good friends since she met him and his friends. Unfortunately when she later returned to her Barian identity as Marin alongside her brother, she then turned against Yuma & the others. In her first duel after reassuming her identity as Marin, she was pit against Bronk, and defeated him as mercilessly as any enemy. She came to regret this decision and shed a tear after defeating Bronk, while he was sacrificed to Barian World.
Despite the two being enemies, they don't have negative qualms towards each other. Dumon felt that if she and Shark were really Marin and Nash he could never hold a serious grudge against them due to their lost memories of their true Barian identities. Meanwhile during her comatose state after the encounter with Abyss, Rio had no reason to oppose him when he successfully attempted to convince the siblings that they were the missing Barians he was looking for, meaning he was trying to help them.
Her and Tori became good friends on her first day back to school and they talk on friendly terms. Despite the different interests, Tori is more impressed with Rio than she usually is with Yuma because Rio's athletic skills speak for themselves. She accompanied her and the others to Sargasso to rescue Ray and watched the duels that Reginald, Kite and Yuma went through together.
Like most of her fellow Barian Emperors, Rio or rather Marin is distrustful to Vector. After Vector had decided he'd been through listening to Nash, he threw Marin off a cliff knowing that Nash would follow suit. After regaining her memories as Marin, she and Vector redeveloped their indifference towards each other as people, merely considering one another a tool to be discarded at one's leisure. Unfortunately, none of the others had known about Vector's hostile takeover and when Marin and Dumon were the first to oppose him, he took great pleasure in targeting Marin for all of his attacks during their duel.