In a world where every fifteen-year-old receives a unique skill, a young man named Chamber is granted the ability Level Up. To his party, Akatsuki, this mysterious skill with no apparent immediate effect seems worthless. Believing Chamber to be a liability, the party, composed of other youths who all acquired powerful and flashy abilities, expels him from their group.

Abandoned and forced to work as a solo adventurer, Chamber continues to operate in the city where Akatsuki is a prominent force. In the course of his solitary adventures, he begins to uncover the true nature of his dismissed skill. He discovers that Level Up possesses a powerful, unacknowledged effect: the more enemies he defeats, the higher his level rises and the stronger he becomes. Realizing that his skill was never a failure, Chamber finds a new path forward. His journey for strength leads him to a fateful encounter with a girl, setting him on a new course to prove the true value of his ability and pursue ever-greater power.