In a world transformed by mysterious objects known as “Custodians”—enigmatic relics capable of triggering phenomena beyond human understanding—humanity now lives divided between two realms: the Overworld, a vast metropolis built upon prosperity, and the Underworld, a wasteland scarred by ruin. Tetsuka, a member of the special unit tasked with retrieving these Custodians, carries out dangerous missions in the Underworld. But beneath his duty lies a personal quest: to uncover the truth behind the disappearance of his sister… A dark, high-stakes sci-fi fantasy of survival, mysteries, and hidden bonds begins!