A world where dungeons have appeared and humans have acquired magical powers... here, the amount of magical power one is born with is an indicator of one's strength. Kai Amachi, the weakest adventurer with little magical power, is braving the dungeons to earn money for the medical expenses of his sick sister, Nagi. However, Nagi's condition suddenly takes a turn for the worse. A huge amount of money is urgently needed for her treatment...!? In dire straits, Kai recklessly participates in the survey of an unknown dungeon with a large reward at stake...

(Source: Overlap, translated)