F-rank explorer Iori Kisaragi is not only dumped by his girlfriend—his childhood friend—but his party leader, Todo, steals her.

Of course, he is also expelled from the party, but he holds a secret vow.

His mother was one of the pioneers in explorer research, but tragically, her paper was unjustly branded as a fraud.

To clear his mother's name, he sets his sights on becoming the strongest explorer. The key to vindicating his mother's reputation lies precisely in his F-rank status.

What makes F-rank truly the strongest?

What awaits Iori as he strives to become the strongest dungeon explorer?