Ritsuka Aoyagi is alone in the world--never fitting in at school and alienated from his own past by a fragmented memory. When his beloved older brother is brutally murdered, Ritsuka is heartbroken but determined to find answers. His only lead is Soubi, a mysterious, handsome college student who offers him an intimate link to his brother's other life: a dark and vibrant world of spell battles and secret names.

Through a video game, Ritsuka tracks down Septimal Moon, the organization responsible for his brother's death. Meanwhile, Soubi fights against two units that both call themselves "Zero" and who claim to feel no pain.