Kouyou Hibiki is a character exclusive to the Yu-Gi-Oh! GX manga. Kouyou was once a three-time Duel Monsters champion who met Jaden in hospital. He taught Jaden everything he knew about dueling and to always have fun dueling no matter what. He challenged Jaden to a duel and defeated him, and when he did he gave him his deck (Kouyou played an "Elemental Hero" deck which contained Winged Kuriboh) and his lucky red jacket. For further elaboration on this, see the spoiler. He is the younger brother of Midori Hibiki.

Spoiler

The reason why Kouyou was in hospital was because he lost a Shadow Game to a mysterious duelist and he found that every time he drew a card while dueling seriously, the deck of his heart would be depleted, and eventually he would die. He decided to give up pro-dueling and make Jaden his final opponent. When he defeated Jaden, he had drawn his last card and fell into a permanent coma.