Ryota Kajiki, or Mako Tsunami in the English anime, is a friendly, honorable duelist who encounters Yugi and company in Duelist Kingdom. They meet after Jonouchi and Honda try to steal the fish he has left cooking over a fire. At first Kajiki is angry, but when he learns that they are friends of Yugi, he is happy to share his catch with them.
As they talk, Kajiki reveals why he has entered the tournament; his father, who taught him how to sail and fish, was lost at sea when Kajiki was a kid. He had tied his son to the mast of their boat, but when the storm was over, the lifeboat was missing. Kajiki is convinced his father is alive somewhere and wants to win the prize money so he can buy his own boat and search for him.
During Battle City, Kajiki duels Jonouchi.