Darkness and light are one. When the light is strong, darkness disappears, and when darkness deepens, light sleeps. A good person cannot endure darkness for long and will eventually turn towards the light. "The moment the darkness in the human heart surpasses the light, the logic of the world must be realigned." Light and darkness are fundamentally one existence, X-White and X-Black. They make a bet over humans. The human who becomes the subject of the bet is John Faust, a promising Wall Street stockbroker, who is always accompanied by Gretchen. However, everything changes after the stock market crash of Black Monday... As John, who has lost everything and fallen, sinks into despair, X-Black approaches him and extends a hand of temptation. Despite Gretchen's attempts to dissuade him, John accepts X-Black's offer and is gradually consumed by him. The more John falls, the more Gretchen's mind and body deteriorate. Through John's actions of even trying to turn away from Gretchen, his last will of goodness and his most beautiful existence, X-Black becomes convinced of his victory.