Mizuno Yūnoshin, a young samurai from a financially struggling lower-ranking family, enters the Ōoku voluntarily. He seeks payment for his sister's dowry, accepting a life of service and isolation within the shogun's inner chambers. Labeled a "country bumpkin" upon arrival, he endures hazing and intimidation in the highly stratified, secretive environment. He witnesses the constrained lives of the men there, described as "vain and wasteful," kept as symbols of political power. Mizuno demonstrates resilience by forcefully defending himself against attempts by other chamber members to initiate him through sexual assault. His reputation rises significantly after he defeats a highly ranked practitioner in a fencing match, showcasing exceptional skill. This victory elevates his status. Reflecting his preference for simple, direct expression, he requests and wears distinctive all-black clothing, setting him apart. Following the death of Shogun Ietsugu, the new shogun, Yoshimune, selects Mizuno as her first concubine. This selection carries a death sentence, as tradition demands the execution of the first man to bed a virgin shogun to preserve her purity. Mizuno accepts this fate with solemn resignation, his primary regret being his inability to see his childhood sweetheart, Onobu, again. During his night with Shogun Yoshimune, he learns her given name is also "Nobu," the same as his beloved. He requests and receives permission to call her by this name during their encounter. Unwilling to execute him, Yoshimune stages a fake beheading. Mizuno is secretly released from the Ōoku, presumed dead, and given a new identity. Freed, he returns to his hometown and reunites with Onobu, fulfilling his deep-seated wish to be with her. His story arc concludes with this reunion; he does not feature prominently in subsequent narratives focusing on earlier periods of the Ōoku's history.