One day, in Japan on an Earth where monsters and dungeons suddenly appeared worldwide, Masato Sato registered as an explorer to make his high school debut.

However, what he discovered through the aptitude test was a pathetic status: no levels, skills, or stats. Though Masato was on the verge of despair, when he actually awakened, an entry called "Proficiency" appeared on his status screen.

Clinging to a sliver of hope, he decided to try mastering Proficiency.

However, Masato, who couldn't truly be called an explorer without levels, skills, or stats, got nervous and failed his high school debut.

And as he went about conquering dungeons as a loner, he remained unaware that he was already the strongest.

*Also serialized on Kakuyomu (content differs)*