Kurumi Mirai is in the first year of high school. She has enrolled in junior high section of the Redrun Magic School, the world's only facility for mages that approved by International Mage League and able to work under royal families when graduates, and she was always top of the class. However, when she applies for the high school section and took the examination to get into a mage training class "Ma-gumi (Mage Class)", she wasn't able to get in in spite having full scores and was top of the class for the whole three years. There are some students in the class next to her that takes that class. Among that there's someone she admires. How will Kurumi Mirai who has extraordinary brain but didn't get in to be a mage candidate try to overcome and grow up? What is the aim for Minami Suzuki, a loyal mage who suddenly appears to be the homeroom teacher? This is a relaxing story of her growth. (Source: MAL News)

The "Labyrinth" is an expansive space deep underground where humans live in clusters known as "colonies." Over the years, the surface has become a distant memory—even perhaps only a fantasy to those who have never experienced its wonders. Making sure humanity survives the harsh conditions of the underground, a colony's citizens can take on a variety of specialized jobs. These include "Workers," who mine precious ore to fuel the colonies, and "Markers," who journey into the Labyrinth's surprisingly lush environment to bring back information that eases navigation. However, humanity also faces a threat to its existence—creatures called "kaijuu" whose sizes range from that of a small child to an enormous building, and are hostile to any human they see. Moreover, kaijuu that are large enough can force their way into the colonies, further increasing their threat level. Memenpu is a nine-year-old college graduate whose inventions have greatly benefitted the Workers in her local colony. Recently, however, she has been dreaming of a place with a neverending ceiling not bound by bedrock. These aspirations fuel her desire to become a Marker and explore the Labyrinth's vast unknown in search of such a fantastical place. Despite her father Gagumber's vehement disagreement, a certain incident with the kaijuu jumpstarts a dangerous yet exciting adventure that will surely alter humanity's course forever.