Kotarou is a young orphan who lost his mother at birth and his father when he was six years old. After being told to flee the monastery where he lived, he becomes the target of Ming Dynasty assassins and the soldiers of Lord Akaike. His blood is prophesied as the key ingredient for an elixir of immortality, which is why he is so relentlessly pursued. Throughout his flight, he is accompanied only by his loyal dog, Tobimaru. Kotarou's personality is marked by a deep wariness and distrust of others, a direct result of the trauma of being orphaned and hunted. He is determined to survive and fiercely protective of Tobimaru, who is his only remaining family. His primary motivation is simply to escape his pursuers and find safety. When he encounters the nameless ronin Nanashi, Kotarou hires him as a bodyguard, beginning a transactional relationship that gradually becomes a deep bond of genuine trust and mutual protection. Kotarou serves as the catalyst for the entire story, as his plight gives Nanashi a new purpose and forces the warrior to confront his own past. The betrayal of the monk Shouan, who hands him over to the Ming, deepens Kotarou's understanding of the world's cruelty, yet he never completely loses his will to fight. Over the course of the film, Kotarou develops from a frightened child who relies entirely on others into a courageous and determined boy. By the end, it is Kotarou who takes the initiative, carrying the wounded Nanashi and Tobimaru toward a new life, demonstrating his growth in resilience and inner strength. His greatest abilities are not martial but emotional: his unwavering loyalty, his perseverance in the face of overwhelming odds, and his capacity to inspire a lost and broken man to seek redemption.