Kengo Fukusuke, an ordinary middle-aged salaryman, is suddenly summoned to another world after getting caught up in a hero summoning meant for a group of high school students. While the teenage heroes are granted overwhelmingly powerful stats, Kengo receives nothing but the universally possessed skill “Language Comprehension.” Deemed useless, he is cast into the “Abyss,” a place from which no one has ever returned. Determined to find a way out, Kengo wanders through the darkness—only to be helplessly attacked by the colossal monsters that dwell within the Abyss…!? A super-ancient technology fantasy that begins from the very depths of the Abyss!