Set in Edo-period Japan, the series follows Mizu, a mixed-race samurai master of the sword who lives a life in disguise while seeking bloody revenge against the four white men who remain in Japan illegally after the borders were closed in 1635, one of whom is her biological father. Along her brutal journey, Mizu forms unlikely alliances with a cheerful aspiring samurai named Ringo, a fallen noble named Taigen, and a disgraced lord, all while evading deadly assassins and uncovering deep conspiracies.