Sakugan

In the vast "Labyrinth," which is located deep down, people are grouped together and called "colonies." The surface has gradually faded into obscurity over time, and to those who have never witnessed its grandeur, may even just exist in their imaginations. A colony's residents can take up a range of specialized jobs to ensure mankind survives the harsh underground circumstances. These include "Workers," who dig up priceless ore to feed the colonies, and "Markers," who travel into the surprisingly rich environment of the Labyrinth and return with knowledge that makes it easier to navigate. The existence of humanity is threatened by creatures known as "kaijuu," who can range in size from a little child to an immense structure and are hostile toward any human they come into contact with. In addition, sufficiently huge kaijuu can break inside the colonies, greatly raising the threat. Memenpu, a nine-year-old college graduate, has made numerous inventions that have helped the Workers in her community colony considerably. She has, however, recently been having dreams about a location with an endless ceiling that is not constrained by bedrock. Her desire to become a Marker and traverse the vast unknown of the Labyrinth in search of this mythical location is fueled by these goals. Despite her father Gagumber's adamant opposition, a specific encounter with a kaijuu sets off a perilous yet thrilling voyage that unquestionably changes the path of human history for all time.