Having spent his childhood in the slums, Hajime Shinonome desperately sought strength to survive. Now, he enjoys a peaceful and carefree life as a resident adventurer of the Komai Village. One day, during a quest, he ventured into a dungeon and finds a young girl being partially eaten by a weakest kind of monster, a slime! The girl's name was Lirui. Having been abandoned by her parents, she had no place to go and entered the dungeon alone in order to stay alive. Hajime couldn't just leave her there, so he took her back to the village to live with him!