In a world where dungeons have appeared and humanity has gained magical powers, one's innate magic capacity determines their strength. The weakest explorer, Hai Amachi, possesses barely any magic power, yet he continues to challenge dungeons to earn money for the treatment of his bedridden sister, Nagi. However, Nagi’s condition suddenly takes a turn for the worse, and an urgent need for a massive sum of money arises. Cornered and desperate, Hai recklessly joins a high-risk investigation of an unknown dungeon that offers an enormous reward... but what awaits him in its depths?
