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.

Although Natsuo and Youji have transferred to Ritsuka's school to monitor him in the wake of his brother's bloody homecoming, the unit named "Moonless" manages to isolate Ritsuka in order to propose a scheme to turn brother against brother.