Yasuri Shichika, a swordsman who fights barehanded using the Kyotouryuu style, lives in exile on a remote island with his sister Nanami until the shogunate strategist Togame arrives with a mission: collect twelve Deviant Blades forged by the legendary swordsmith Kiki Shikizaki. Each blade has a current owner unwilling to part with it, and each carries a supernatural poison that warps whoever wields it. Shichika agrees, not for duty or glory, but because Togame tells him to fall in love with her.