Gengetsu Kibaoni was originally a warlord in the Sengoku Era of Japan renowned for his cruelty and brutality. Gengetsu sought to unite Japan under him through fear until his reign was put to an end when he was assassinated by ninjas from the Igasaki Clan. However, before dying, Gengetsu vowed to come back and conquer the world through terror.
444 years later, Gengetsu reincarnated as a demon along with his three generals and returned to cause destruction until he was defeated and sealed away by Yoshitaka Igasaki with the 48 Sealing Shuriken.
However, by 2015 the seal wore off and Gengetsu was freed by Kyuemon Izayoi, though he was unable to assume a tangible form. Gengetsu thus ordered Kyuemon and his forces to gather enough Power of Fear from humans in order to fully revive him. To accomplish this task, Kyuemon used the corrupted Sealing Shuriken to create Youkai and revived Gengetsu's other top generals.
After Kyuemon revived Masakage Tsugomori, Gengetsu appeared before his army and, delighted at the terror they had spread, told them to gather more fear in order to resurrect him. Gengetsu later intervened to personally create a Youkai from two of the Sealing Shuriken at the request of Masakage. By combining two Sealing Shuriken with a toolbox, Gengetsu created the powerful Advanced Yokai Nue.
Gengetsu was later contacted by Masakage again, who asked his permission to summon more Advanced Youkai. Gengetsu agreed and bestowed his power onto ten of the Sealing Shuriken. He also told his wife Ariake no kata not to cause trouble for Masakage.
Gengetsu was later fully revived after the death of his son, Mangetsu Kibaoni, when Kyuemon used Ariake no kata's despair over the loss to revive him. Kyuemon was also revealed to be Gengetsu's illegitimate son, whom he had sired with a concubine. In the final battle against the Ninningers, Gengetsu absorbed Kyuemon to become more powerful but Kyuemon, encouraged by Ninningers' declaration that they were fighting because they chose to and not because of their family lineage, broke free of Gengetsu. Gengetsu was then defeated by the Ninningers in Gekiatsu Dai-Oh with Gekiatsu Dai Fever.