In Edo-period Japan, the Yamashiro clan mines gold in secret and ships the treasure to the Toyotomi Shogun of the Dark for protection. The Shogun of the Dark plans to use that gold to buy advanced Spanish weaponry and topple the Tokugawa Shogunate, reshaping Japan’s power from the shadows. A violent storm drives the shipment ashore onto Mochizuki territory, and the Eight Devils of Kimon—an infamous ninja unit with supernatural abilities—slaughter the people of Shimoda Village to keep the gold’s location hidden.
During the investigation, a Mochizuki Kōga ninja team is wiped out by the Devils. The sole survivor, the kunoichi Kagero, Emi Shinohara, is captured by Tessai, Ryuuzaburou Ootomo, who attempts to rape her. She is rescued by Kibagami Jubei, Koichi Yamadera, a mercenary ex-Yamashiro ninja who fights fiercely and eventually kills Tessai. To force Jubei’s cooperation, Dakuan, Takeshi Aono, a Tokugawa spy, blackmails him into assisting with the mission to eliminate the remaining Devils, stabbing Jubei with a poisoned shuriken and promising an antidote once the job is done. Jubei learns from Dakuan that the Devils are led by Gemma, Gemma’s alias as the immortal Genma Himuro, a former Yamashiro ninja who had ordered his team to kill each other five years earlier to conceal the gold’s location; Jubei had decapitated Gemma in revenge, but Gemma survives due to his apparent immortality.
The trio presses on as Benisato, Gara Takashima, launches a late attempt to kill Jubei, only to be felled from afar by Yurimaru, Toshihiko Seki, Gemma’s right-hand man, for failing her mission. Kagero agrees to work with Jubei and Dakuan, who reveals a deadly secret: Kagero’s body contains toxins so potent that anyone who kisses or sleeps with her dies, a danger that also explains why Jubei survived Tessai’s attack. The danger becomes personal as the trio reaches Shimoda and discovers the villagers died from a poisoned water supply, making it look like a plague.
In Shimoda, Jubei and Kagero fend off attacks from Mushizō, Reizô Nomoto; Zakuro, Masako Katsuki; and Utsutsu Mujūrō, Norio Wakamoto; Jubei destroys Mushizō and Utsutsu while Kagero’s wits help them survive. They locate the beached ship, and Kagero deduces that the gold has been moved to Kashima Harbor, where it will be loaded onto another vessel bound for the Shogun of the Dark.
Arriving at Kashima, the town is evacuated out of fear of the plague. As Jubei battles Shijima, Akimasa Omori, Kagero sends a message to Sakaki Hyobu, Shûichirô Moriyama, urging him to bring his army to the harbor. Dakuan adds that the antidote to Jubei’s poisoning can only be found if he sleeps with Kagero, a revelation that complicates every choice. When Kagero is captured by Shijima, Jubei defeats him and rescues her; she asks him to consummate their bond to cure the poison, but he refuses. As the Shogun of the Dark’s envoy arrives by ship, Jubei departs to keep the gold from reaching its destination.
Kagero undertakes a final confrontation with Sakaki Hyobu, but he stabs her, revealing himself to be Gemma in disguise after having murdered the real Sakaki Hyobu days earlier. Enraged, Jubei fights through waves of ninjas, and Yurimaru is killed by a gunpowder-rigged rat set by Zakuro for rejecting her advances, allowing Jubei to escape. He finds Kagero mortally wounded; she admits her love for him, and they share a kiss that cures Jubei’s poisoning. Before dying, Kagero gives Jubei her headband, a final keepsake of their bond.
On the departing ship, Gemma unveils his true plan: to use the gold to raise a ninja army to terrorize Japan rather than aid the Toyotomi. He murders the envoy who confronts him, and, as a dramatic gambit, sets the ship ablaze. The gold becomes molten and engulfs Gemma, who sinks into the seas. Dakuan thanks Jubei for his humanity and his sacrifice, and Jubei resumes a vagabond life, with Kagero’s headband tied to the hilt of his sword as a reminder of the bond they shared.
