In the depths of the underground Labyrinth, where human colonies thrive, the surface world is a distant memory. Life revolves around specialized roles like the ore-mining Workers and the exploration-savvy Markers. Yet, amid this struggle for survival, the looming threat of kaijuu—monstrous creatures hostile to humanity—haunts every soul. Enter Memenpu, a brilliant young inventor yearning for the untamed expanses of the Labyrinth and its unknown mysteries. Against her father's wishes, an encounter with a kaijuu propels her into a perilous yet thrilling journey that could reshape the fate of humanity forever.