Allen Walker gets off a train and arrives in a town where a ghost has been rumored to be haunting a nearby church. Anyone who investigates it simply disappears. So a couple of police officers decide to check it out, but one of them dies and the other is saved at the last minute by Allen himself. The white-haired boy claims to be an exorcist, but no one really believes it. However, the policewoman decides to head back into the church with Allen to find out what killed her partner.
Later, they find themselves face-to-face with the monster that Allen calls an "akuma," a strange armored beast that was created from a bonded soul and forced by an entity known only as the Millennium Earl to continue killing and grow stronger even as it felt remorse and regret for being forced to kill others. Allen unleashes his power upon the akuma and frees the trapped soul inside, killing the akuma.