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.

Ritsuka's faith in his older brother Seimei is pushed to the limit when the unit named Moonless reveals sordid details of Seimei's horrific past deeds. Then, while Ritsuka is still reeling, the unthinkable happens: Seimei returns to reclaim Soubi.