Ren and Rai are two unfortunate souls holding a secret war with a society of people that covertly corrupt innocent humans, taking their souls and demonizing them in exchange for fulfilling their wishes. Those that lose themselves are said to have fallen to Diablo. The two discover untold truths about the group, and something else about their own haunted past, where they lost Mio, a girl dear to them, whose disappearance branded them murderers.