One day while questing, he entered a dungeon and discovered a young girl being partially devoured by the weakest monster type - a slime.

A teenager summons the courage to help a friendly robot known as A.R.I. kidnapped by a ruthless lab director working for a powerful corporation seeking to turn him into a dangerous weapon in order to rule the world.

When Tsukune accidentally enrolls in a school for monsters disguised as humans, he must hide the fact that he's really human or risk losing his life.