A boy who died after being bullied and pushed down a flight of stairs is reborn in another world as a catkin, a race considered the weakest in terms of physical strength, magic, and intelligence. Now named Nyango, he possesses a rare and unique magical attribute known as the empty attribute or sky attribute, which is initially ridiculed as being completely useless. Despite this enormous handicap, he aspires to live a carefree life as an adventurer.

Through his own ingenuity, Nyango learns to harness his seemingly worthless magic to create weapons and armor from the sky itself, eventually developing the ability to walk on air. As he grows, supported by the kindness of those around him, he begins to unlock the true potential of the sky attribute, setting him on a journey to become the strongest catman adventurer. The story follows his early adventures, including fleeing from goblins and engaging in desperate battles against kobolds, all while exploring dungeons and the wider fantasy world.

One significant narrative arc involves the exploration of a dungeon that is revealed to be an ancient, buried shopping mall and its surrounding skyscraper towers. Inside this ruin, the party discovers an ancient bookstore containing books with pictures of humans, raising mysteries about how this entire section of land became buried and what happened to the humans who once lived there. The story also touches on darker social issues, such as the exploitation of catkin characters, including an incident involving Nyango's older brother who was forced into sex work before being rescued. Later arcs feature encounters with anti-royalty revolutionaries, including a catkin suicide bomber whom Nyango stops, as well as a dangerous magic-strengthening technique involving consuming monster hearts that results in catastrophic side effects for those who attempt it.