Plot
In Edo period-Japan, the Yamashiro clan (山城藩) mines gold in secret, and sends a shipment to the Toyotomi Shogun of the Dark (闇公方) as payment for his protection. The Shogun of the Dark intends to use the gold to buy advanced Spanish weaponry and overthrow the current government, the Tokugawa Shogunate. The ship runs aground onto Mochizuki territory (望月藩) in a storm, and the Eight Devils of Kimon (鬼門八人衆), a ninja team with supernatural powers in the employ of the Yamashiro, kill the people of the nearby Shimoda Village (下田村) to keep the gold shipment a secret.
While investigating the deaths, a Mochizuki Kōga ninja team is massacred by the Devils. The sole survivor, the kunoichi Kagero (陽炎), is captured by a Devil, Tessai (鉄斎), who attempts to rape her. She is rescued by Kibagami Jubei (牙神 獣兵衛), a mercenary ex-Yamashiro ninja, who fights and eventually kills Tessai. Dakuan (濁庵), a Tokugawa spy, blackmails Jubei into helping him kill the remaining Devils. To ensure his compliance, Dakuan stabs Jubei with a poisoned shuriken, and promises to give him an antidote once the mission is complete. Jubei learns from Dakuan that the leader of the Devils is Himuro Gemma (氷室 弦馬), the former Yamashiro ninja leader, who had ordered his team's members to kill each other to cover up the location of the goldmine five years earlier. Jubei, who had been forced to kill his comrades to survive, decapitated Gemma in revenge; Gemma survived due to his immortality. Jubei is attacked by another Devil, Benisato (紅里), but he is saved by Kagero; before she can be questioned, Benisato is killed from afar by Yurimaru (百合丸), Gemma's right-hand man, for failing her mission. Kagero agrees to work alongside Jubei and Dakuan, who informs Jubei that her body is infused with such deadly toxins that anyone who kisses or sleeps with her dies, which was why Jubei could kill Tessai.
The trio arrive in Shimoda, where they discover that the villagers died due to their water supply being poisoned, making it appear that they were killed by a plague. Jubei and Kagero fend off attacks from three of the Devils – Mushizo (蟲蔵), Zakuro (石榴), and Utsutsu Mujuro (現 夢十郎); Jubei succeeds in killing Mushizo and Utsutsu. After finding the beached ship, Kagero deduces that the gold has been taken to Kashima Harbor, where it will be transported to the Shogun of the Dark in another ship.
Jubei, Kagero, and Dakuan arrive at Kashima, which has been evacuated due to the townspeople's fear of the plague. While Jubei battles another Devil, Shijima (シジマ), Kagero sends a message to Sakaki Hyobu (榊 兵部), the Mochizuki chamberlain, to bring his army to the harbor. She also learns from Dakuan that Jubei's poisoning will only be cured if he copulates with her – the poisons in her body will counteract his. Kagero is captured by Shijima, and Jubei kills him, rescuing her once more. Kagero asks Jubei to sleep with her to cure himself. He decides against it, and upon the arrival of the Shogun of the Dark's envoy in a ship, he leaves to prevent the gold reaching its destination.
Kagero arrives to meet Sakaki, but he stabs her, revealing himself to be Gemma in disguise as he had murdered the real one days before. Enraged, Jubei fights through waves of ninjas, but is nearly killed by Yurimaru. A gunpowder-rigged rat, left as a trap by Zakuro for Yurimaru for rejecting her advances, kills him, allowing Jubei to escape. He finds Kagero; mortally wounded, she admits her love for him and they kiss, curing Jubei's poisoning. Before dying, Kagero gives Jubei her headband.
Jubei and Dakuan board the departing ship. On board, Gemma reveals his true intentions – to use the gold to raise a ninja army to terrorize Japan rather than serve as an ally to the Toyotomi – to a masked samurai who serves as the Shogun of the Dark's envoy, and proceeds to kill him. During an altercation with Zakuro, Jubei and Dakuan set the ship ablaze. As Jubei and Gemma engage in a brutal fight, the gold becomes molten and engulfs Gemma, who sinks to the bottom of the sea. Afterwards, Dakuan thanks Jubei, and expresses admiration for his and Kagero's humanity. Jubei resumes his vagabond lifestyle, with Kagero's headband tied around his sword's hilt.
