Midori Hibiki (響みどり, Hibiki Midori) is the headmaster of first-year Slifer Red students at Duel Academy and the older sister of Koyo Hibiki in the Yu-Gi-Oh! GX manga. In the English manga, she is usually addressed as "Ms Hibiki". However, Jaden addresses her as "Ms. Midori".
She is a kind person who after seeing how close Jaden became with her brother, began to consider Jaden another younger brother and even gave Jaden his first Duel Disk. She is one of the few Duelists that her brother could never beat even when he went pro. Her skill is shown first hand when she faced Reggie MacKenzie in order to force Reggie to reveal the cause of Koyo's coma. During the Duel Reggie was very nearly defeated without landing a single attack on Midori in only a small number of turns. Only by using blackmail was Reggie able to escape a crushing loss and pull off a win, despite having quite easily dispatched Alexis Rhodes previously and having beaten Midori's former World Champion brother years before (though while controlled by Tragoedia). After Midori is defeated, Reggie reveals that she was lying and doesn't know what happened to her brother despite having been the one that did it. Midori is dismayed at the discovery and quietly asks for her brother's forgiveness, as she falls to her knees. She collapses in Jaden's arms, and is later revived when Jaden defeats Reggie.
Midori plays a "Darklord" Deck, which focuses on the Summoning of high-Level monsters with devastating effects via Trap Cards. A confident Duelist, she signifies the activation of such cards by snapping her fingers.