In a world where creatures called Demon Spirits once existed. Young Alto is pushed into a well that sealed away a Demon Spirit, due to the schemes of his bullies. To survive, Alto consumes the flesh of the Demon Spirit and becomes a demon himself. The Demon Spirit's name was 'Kamikui' (God Eater) - a unique demon that grew stronger by devouring its opponents' flesh. Having inherited the characteristics of 'Kamikui', Alto grows stronger by consuming monsters. While struggling with his condition, Alto searches for a way to become human again to fulfill his promise with his childhood friend Mei.
