25 years ago, the sudden appearance of the Hachioji Dungeon threatened humanity until a legendary hero cleared it, turning it into a peaceful tourist attraction. Today, 37-year-old Eiji Aikawa works as an ordinary, humble salaryman at a dungeon tour company. He bows low and takes disrespect from rowdy youths without complaint until they cross the line. When pushed too far, Eiji unleashes his hidden, terrifying power to effortlessly flatten troublemakers bare-handed! The truth? Eiji, fighting completely unarmed, is the very hero who cleared the Final Dungeon a quarter-century ago. Having kept his distance from dungeon diving, Eiji is drawn back into the dangerous lower depths when Mii, his old comrade's niece, asks for his help!