Ryota Sato finds himself transported to a world where everything drops from monsters in dungeons. 
He and his Ryota Family live their lives venturing into dungeons to sell monster drops. But one day, after rescuing the city of Indole from poverty, Ryota runs into a mysterious girl in the dungeon Aurum. 
"A monster?!" 
"Nope! I'm no monster. My name is Aurum. I am Aurum!" 
Who is this unknown girl, who shares a name with the dungeon she appeared in?!