Constructed solely for war, sayabito are fearsome human weapons who are tightly bonded to those who wield them. In the wake of a great war, fiery and impatient Rivia and her willowy, cautious partner Kuifa roam the land in search of sayabito who lost their wielders in the conflict, in order to register and protect these vulnerable sayabito before they wither away or are exploited. Though Rivia and Kuifa frequently exasperate each other with their clashing approaches, they share one common goal: to carve out a life in the peacetime for which they, and others like them, were never meant.