Zushio Maru, the younger brother of Anju, is born into an aristocratic family led by his father, a steward entrusted with guarding the emperor’s hunting grounds. Raised on teachings of reverence for nature and compassion toward animals, these principles form Zushio’s moral foundation. When a rival official falsely accuses his father of orchestrating a forest fire, the family is exiled. During their flight, Zushio and Anju are severed from their mother and ensnared by slave traders, who sell them to Sansho, a ruthless estate steward.

Enslaved under Sansho’s tyranny, Zushio faces grueling labor and the ever-present specter of torture. Survival hinges on the siblings’ loyalty to each other and clandestine aid from Saburo, Sansho’s empathetic son. Zushio’s resilience battles against despair as systemic cruelty tests his spirit. Supernatural forces—a mystical mermaid and talking creatures—intervene to ease their plight, merging the story’s stark tragedy with ethereal hope.

Zushio’s evolution from endurance to agency peaks when Anju’s sacrifice enables their escape. Vowing justice, he harnesses his aristocratic lineage to petition authorities, ultimately dismantling Sansho’s slave system—a victory mirroring his father’s teachings yet reliant on institutional power. The tale concludes with Zushio reuniting his fractured family, including his blinded mother, honoring bonds strained by loss.

Zushio’s narrative threads themes of perseverance, kinship, and the clash between submission and defiance. Adapted for younger audiences, fantastical allies and symbolic victories soften the source material’s severity while preserving its focus on quiet courage in the face of oppression.