In a post-apocalyptic world ruled by the so-called "Numbers," every person's identity is marked by their own "Number," which can define any aspect of their lives. It could be the distance they walk or the number of compliments they receive from others; when this 'number' drops to zero, it could lead them to the edge of a cliff. In the year 305 of the Alcian calendar, Hina inherits a mission from her mother, whose number has fallen to zero: to search for the legendary Red Baron. During her adventure, she will meet a half-masked swordsman who tries to hide his identity because he is recognized as degenerate due to his incredibly low 'number.'
