Black God follows Ibuki Keita, a high school student whose life has been shadowed by relentless bad luck for as long as he can remember. Tragedy seems to follow him wherever he goes, and the people around him often end up dead, leaving Keita isolated and unwilling to grow close to anyone, even his childhood friend Akane. Unable to escape a life of misery and disgrace, he drifts through each day expecting the next disaster to be even worse than the last.
One night, while eating at his favorite ramen shop, Keita meets Kuro, a strange girl whose abilities far exceed those of an ordinary human. Kuro reveals that she is a Mototsumitama and explains Terra, a life-energy force split among three identical people, as well as the global Doppeliner System and the role of the Coexistence Equilibrium, the beings who protect Terra’s flow around the world. Keita refuses to believe her at first, but when he is dragged into the crossfire of this hidden conflict and left on the verge of death, he makes a contract with Kuro. From that moment on, he is bound to her and must stay by her side at all times, even as the truth of that bond begins to reshape his fate.