In a world where dungeons and monsters appeared one day and people began to develop special powers, Yuto Kirishima is an orphan and an F-Rank adventurer who is forced to join lower-level raids to make ends meet as he supports his younger sister, Arisa. When his guild tries to turn him into a human sacrifice, he instead awakens to an overwhelming new power! As he uses this legendary sage skill to raise his rank, he suddenly hears news of a dungeon break right by his sister's school. Can he save her and the city before it's too late?