ーGod is dead. The most sacred, powerful being in this world. It bled under our knives. In her dream, Orihara Saki, an ordinary high school girl, witnessed the end of the world. As if responding to the dream, Saki is attacked in reality by a human-devouring monster called the Heart Scar Bug. At that moment, Saki grasped... a "sword of lone being". Orihara Saki, an ordinary girl, and Matoi, the girl with the God-slaying sword. This encounter eventually leads Saki to a battle with the Heart Scar Bug and God's kin, the Ark of God. To prevent the end of the world. It is the apocalypse of a world without gods.