Reginald Kastle, known as Ryoga Kamishiro (神かみ代しろ 凌りょう牙が, Kamishiro Ryōga) in the manga and Japanese version and nicknamed "Shark" (シャーク, Shāku) in all versions, is one of the main characters in Yu-Gi-Oh! ZEXAL. He is one of Yuma Tsukumo's close friends and rivals. He was originally an arrogant and callous person, but has grown quite humble. He is later revealed to be Nash (Nasch (ナッシュ, Nasshu) in the Japanese version), the leader of the Seven Barian Emperors. Determined to not let tragedies befall his people again, he betrayed Yuma and his friends to safeguard the Barian World. He is the only Barian Emperor not to be absorbed by Don Thousand, as well as being the only Barian whose original memories were not altered. He later vanished after losing to Yuma in a Duel that had the Human and Barian Worlds at stake. He along with the Seven Barian Emperors were revived by the Numeron Code.
Mixels Fanon Wiki Description
Reginald Kastle (AKA Shark/Nash) is a duelist in Mixels-Yu-Gi-Oh, but is NOT seen dueling ANYONE. He makes cameo appearances sometimes in the "Wiki show".