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.
A mix-up at a coffee bar sends Kuifa and Rivia on the run, but it seems Kuifa’s body is beginning to betray him. He comes down with a fever and is now immobilized, leaving Rivia to make decisions and face vicious creatures on her own. Alone for the first time in a long while, Rivia begins to question just how little she knows about Kuifa, about sayabito, about herself… As political unrest stirs back at Protettori headquarters, a mysterious sayabito finds work watching over a newborn boy—leading to a decades-long bond that will change the course of the man’s life forever.