These are two sides of the world. In the darkness of the world, there lives a group of monsters that look like humans but are not human. They make a living by absorbing the power of human brains, and they are called demons. Facing the attack of the demons, the top management of mankind established a special organization 'G'. They mainly fight against the demons, and there is also a group of mysterious people. No one knows where they come from, they only know that they are the demon slayers.