Zen was a demon of infirmity living in the hell. Through his life he had seen too many torments. Hell is a dark place where suffer never ends. It's fulled with noises of screaming and whinning. The hell worms endlessly devour the flesh of tainted souls. Zen does not like the hell, he wished to get out of the hell. After his 16th birthday, he was given a task by the ruler of hell to spread disease on human world. At first he did not want to accept the task but after being provoked by other demons of his age he accepted the task and venture into the human world.