As children, Rio and her brother, [[Reginald Kastle|Reginald]], lived in a [[Kastle's mansion|mansion]] with [[Mr. Kastle|their]] [[Mrs. Kastle|parents]], where he taught her how to play ''[[Duel Monsters]]''. One night, Rio stole Reginald's Deck as a prank, forcing her brother to chase her for it. They accidentally knocked down a suit of armor, which nearly fell on Rio. Reginald saved her from being crushed, only to acquire a scar on his back. Reginald and Rio were also involved in a car accident that, according to [[Kurage]], killed all of the Kastle family members,<ref name="ep114">{{episode|Yu-Gi-Oh! ZEXAL|114|ref}}</ref> including Rio herself and Reginald. Nasch and Merag then had their souls transferred into the bodies of Reginald and Rio so they could live again, but they somehow survivedwith their parents being the only fatalities.<ref name="ep115">{{episode|Yu-Gi-Oh! ZEXAL|115|ref}}</ref> At another time, Rio and Reginald visited a theme park where the former offered the latter one of [[Kastle twins' rings|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.<ref name="ep78">{{episode|Yu-Gi-Oh! ZEXAL|78|ref}}</ref>