Demak is a Dark Signer bearing the Monkey Birthmark. His color scheme is yellow amongst the Dark Signers and his history is unknown. The source of his rebirth as a Dark Signer is shrouded in mystery and left unexplained, leaving his only tie to the Signer War in Ancient Fairy Dragon - the card he holds after Fudou Hakase dropped it after Rudger’s takeover at MIDS. Using Ancient Fairy Dragon, he lines himself opposite Ruka while his Dark Synchro Monster - Demonic Monkey King Zeman - terrorises the Duel Spirit World which leads Ruka to enter the world while Demak duels Rua who is left in her place. To fit with the monkey theme in his deck and dark power, the Earthbound God Demak possesses is Cusilly, a representation of the Nazca Line that has been forged as a Birthmark on his arm.
Once Ruka returns to the real world following Rua destroying Zeman in the duel, she uses his Power Tool Dragon and her new companion Regulus to regain Ancient Fairy Dragon. Using the two, she destroys Cusillu, resulting in Demak's death.
After Yusei finishes the duel against Godwin, Demak is revived alongside the other Dark Signers. His story after wards is left untold.
