Genma Wars is set in a post-apocalyptic world, where mankind has been subjugated by a demonical tribe known as Genma. The humans are reduced to little more than slaves for the Genma, who employ mutant armies of cyclopses, vampires, werewolves, highly intelligent simian soldiers, and other mythological beings, to keep the humans at bay. The authoritarian Genma leader, The Maoh King, desires to have an heir with immense, extraordinary power. He orders his men around the kingdom to abduct Hito women, who possess latent powers. The Maoh King is convinced that if he conceives a child with a Hito woman the child will possess amazing powers.
In one case, in exchange for the safety of her village, a Hito girl called Non submit to the Maoh King, and give birth to male twins, Loof and Jin. Loof is taken to grow up among the Genma, while Jin grows up under his mother' care, however she is labelled as a whore by her fellow kinsmen. Eventually, Loof and Jin encounter each other and plan revenge against their hated father. However, their father reveals he only created them, and the whole hybrid Human-Genma, to bring the war across the Earth, out of boredom. He throws his sons in a time portal, back to the present time, when the war was initiated, in order to stop their dystopic world.