Klein Moretti, following an incident of attempted suicide, finds himself losing parts of his memory and slowly becomes entangled in a supernatural world filled with mystery and danger. Originally an ordinary history graduate, he is drawn into the attention of the Night Goddess Church’s extraordinary team—the “Night Watchers”—due to the death of his friends and a mysterious notebook from the “Fourth Epoch.” Through interactions with Dunn Smith, an extraordinary “Night Watcher,” Klein begins to explore the supernatural power brought by potions and gradually uncovers the secrets hidden within the notebook, including the existence of the "Gray Fog World." As he ventures deeper into this world, Klein realizes that this path is filled with unknown fears and unbearable costs. However, driven by a desire for truth, he chooses to continue forward, embarking on a journey woven with the extraordinary and a destiny yet to be unveiled.