Keita Ibuki, a freelance game programmer scraping by in Tokyo, learns that every person is born one of three identical Doppeliners who secretly share a single fate. Guardians called Mototsumitama hold the world to a balance known as the Coexistence Equilibrium. His ordinary life ends the night he takes a fatal wound and Kuro, a young Mototsumitama, saves him by binding the two of them under a contract. With his childhood friend Akane Sano caught up in it, Keita is drawn into the Kaionji Group's move against that balance.