This suspicious person is about to become a legend.” A young man, Nagano, vanished after challenging a dungeon that suddenly appeared in modern times. He survived for 25 years in its uncharted depths, eating ferocious monsters and gaining an incredibly powerful body. When he finally returns to the surface, he finds himself in a future Japan where dungeon streaming has been made mandatory. His rampage, which surpasses even disaster-class monsters, is immediately streamed, and he quickly joins the ranks of top explorers. Armed with 25 years of experience, Nagano rises to become a legend of this new era.