Marquis Yanus is a villain in the anime and manga Great Mazinger. She is a witch in a long red dress with horn-shaped purple hair, reminiscent of the headdress of Maleficent. She carries a white wooden staff, and has a black cat perched on her shoulder. Her various "witchcraft" powers include flight, teleportation, invisibility, and the ability to control people by jamming an electronic spike into their heads. Like the rest of the Mikenese, Marquis Yanus has two faces; at various times, her head spins 180 degrees, hiding her "beautiful" face and revealing the hag-like "evil" face that is usually concealed under her hair.

She first appeared in the 22nd episode of the Great Mazinger anime as a replacement for Archduke Gorgon after Archduke Gorgon was accidentally killed by Great Mazinger in the previous episode. As Archduke Gorgon did before her, she retains Minister Argos as her chief adviser.

Marquis Yanus has her own mecha, which is roughly the same size as the Mikenese Generals and Great Mazinger, and resembles a demonic version of herself. The mecha's cockpit is in its left breast.

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