On his first day at a new school, twelve-year-old Ritsuka Aoyagi meets Soubi Agatsuma, a mysterious young man who says Ritsuka's recently murdered older brother Seimei assigned him to protect the boy. Soubi declares himself Ritsuka's Fighter, partner in spell battles waged through carefully chosen words, with Ritsuka as his Sacrifice. Two years of Ritsuka's memory are simply gone, and bearing the true name Loveless, he follows the trail toward the organization Septimal Moon to learn who killed Seimei and why.