Jirō, a young boy of
Japanese and
Ainu descent, is a
foundling raised by a kindly
innkeeper and her daughter in the village of
Sai on the
Shimokita Peninsula. One evening, a
shinobi kills Jirō's adoptive mother and sister while he is away. When he returns home, he finds their bodies and a strange dagger. The angry villagers accuse him of the murders, and rather than face a brutal
crucifixion for the grave crime of
parricide, Jirō escapes with the dagger. He encounters a
Buddhist monk called
Tenkai, who works for the
Shogunate as an
Oniwaban (Secret Police). Tenkai takes the boy to confront the man who supposedly killed his family and provokes him into delivering the killing blow. To cover his tracks, Tenkai has the village set ablaze, and the villagers are slaughtered. Tenkai takes Jirō to his temple on the island of
Ezo, and has his subordinates Shingo and Sanpei train him in the ways of the Ninja. Years later, Jirō leaves to find answers to the mystery of his family and his father, Tarōza. Meanwhile, Tenkai has him followed. Jirō comes across a group of Japanese men beating up an old Ainu man, and he quickly dispatches them. The old man dies of his injuries, but his son Uraka takes Jirō to his home village of Shinopirika-Kotan, unaware the old man's assailants are agents of Tenkai. At Kotan, the village elder recognizes Jirō's dagger as the Dagger of Kamui, which was originally owned by a former village chieftain. It was given to a Japanese ninja who married the chieftain's daughter, Oyaruru. Years later, Oyaruru returned to Kotan alone, but eventually left the village to live upriver by herself. Jirō finds Oyaruru and learns she is his biological mother. She reveals that Tenkai dispatched Tarōza to the mountain Kamui Nupuri to find a rumored treasure large enough to keep the Shogunate in power. However, Tarōza broke all contact with Tenkai and married Oyaruru. When Tenkai caught up with them, he slashed the face of the infant Jirō and sent him floating downriver in their canoe. Tarōza fought Tenkai's men on the cliff above, but lost an eye to a primitive grenade and his sword arm to Hanzou, then appeared to fall to his death. Jirō comes to the horrifying realization that Tenkai had tricked him, and that the man he stabbed was his father. During their evening meal, Jirō and Oyaruru collapse from a paralysis potion supplied by Shingo, and Oyaruru is killed by Shingo with the Dagger of Kamui. Implicated in her murder, Jirō is imprisoned, but Uraka returns to help free him. Jirō finally realizes that Tenkai has been manipulating him for years into following his father's footsteps, searching for the treasure, and plans his revenge against Tenkai. Traveling north, Jirō is befriended by the elderly Andō Shōzan and a young Ainu girl. She helps find secret instructions to find a great treasure which is hidden with the hilt of the sword of Kamui. However, Jirō is tracked down by three of Tenkai's formidable assassins, whom he defeats, but not before they kill Shouzan. The Ainu girl helps Jirō escape, but she kills herself when confronted by the following Tenkai. With the aid of the sailor Sam, Jirō books passage on Captain Drasnic's ship to the United States. Onboard, he is attacked by Oyuki, one of Tenkai's shinobi, but he defeats her. He then saves her from drowning, and they develop a strong bond. After arriving in America, Jirō, Sam, and Oyuki become separated, and Jirō travels on alone. Jirō befriends Chico, a French-born Indian woman, and shelters with her tribe. He then encounters
Mark Twain on the way the
Los Angeles, heading for the island of
Santa Catalina, which is apparently the location of
Captain Kidd's treasure. Jirō eventually finds a small treasure on the island, but Tenkai and his shinobi have followed him there with Oyuki. Tenkai suddenly reveals that Sanpei is a Satsuma and an associate of Tarōza, who was also Oyuki's father, making her Jirō's half sister. Oyuki angrily stabs Tenkai through the heart with the dagger, although he manages to fatally wound her before he dies. Jirō then finds the real treasure below in a hidden cavern. Later, Chico reappears and shows Jirō a similar copy of the treasure's location. She reveals her real name is Julie Rochelle, the daughter of French spies also seeking the treasure, and that her father and Tenkai killed each other. Jirō now realizes that Tenkai has been using body doubles. He returns to Japan, where he uses Captain Kidd's treasure to help fund the overthrow of the Tokugawa shogunate by the combined
Satsuma-
Choushuu forces. In 1869, at the
Citadel of Hakodate, the Imperial Japanese Navy and Army closed in on the last remaining Shogunate rebels. After a massive
naval bombardment, Jirō wanders through the rubble and bodies, eventually encountering Tenkai. They engage in battle, during which Jirō kills Tenkai by impaling him through his cranium with the dagger. Jirō leaves Hakodate as the Imperial forces capture the city, but not before paying a silent farewell to Sanpei and his master, the samurai
Saigō Takamori. ==Characters==