Ryuuji Otogi  

Duke Devlin, 御伽 龍児

The individual responsible for developing the Dungeon Dice Monsters game is named Otogi. This person then establishes a competitor's shop situated near Kame Game Shop on the opposite side of the street. Initially, Yuugi and Otogi are not acquainted. However, after Yuugi manages to defeat Otogi in his own game despite lacking prior knowledge about its rules, they become friends.