Set in feudal Japan during the turbulent
Tokugawa shogunate, the story follows Manji, a skilled samurai cursed with immortality. Granted eternal life by a mysterious eight-hundred-year-old nun via sacred bloodworms known as "kessen-chu," Manji’s wounds heal instantly, and he is rendered impervious to death. However, this divine gift is a heavy burden; he is haunted by the wrongful killing of his innocent sister and resolves to atone for his violent past by sending one thousand wicked men to the afterlife.His lonely crusade shifts when he encounters Rin Asano, a fierce young girl whose family was brutally murdered by Anotsu Kagehisa, the ruthless leader of the rising sword-school, Itto-ryu. Anotsu seeks to overthrow and unify all traditional dojos under his radical banner, regardless of the bloodshed required. Seeking vengeance, Rin hires Manji as her bodyguard. Despite initially resisting, Manji sees shades of his deceased sister in Rin and agrees to protect her on her perilous journey across Japan.As Manji and Rin track the Itto-ryu, they encounter a series of formidable and eccentric adversaries. They face the Mugai-ryu, a shadowy counter-group of assassins led by the enigmatic Habaki Kagimura, who serves the shogunate and desires Manji’s immortal blood to unlock the secret of eternal life for the ruling class. Simultaneously, internal conflicts tear at the Itto-ryu. Anotsu’s brutal methods alienate some of his closest followers, leading to bloody betrayals,
psychological torment, and tragic sacrifices.Throughout the violent campaign, Manji pushes his regenerative abilities to the absolute limit, enduring horrific mutilations in brutal, meticulously choreographed sword fights to keep Rin alive. Rin, meanwhile, evolves from a fragile, revenge-obsessed orphan into a resilient warrior, though she wrestles heavily with the moral cost of her vengeance and the cycles of bloodshed she is perpetuating.The narrative culminates in a massive, chaotic siege at Edo Castle, where the Itto-ryu launches a desperate final assault against the shogunate's forces, and the Mugai-ryu makes its final play. In the explosive climax, Manji confronts Anotsu in a grueling, visceral duel that tests both men's ideals and resolves. Amidst the carnage, personal vendettas are laid bare, and the true cost of power and survival is revealed. In the aftermath, with the Itto-ryu dismantled and her vengeance achieved, Rin parts ways with Manji. Left once again to wander the earth alone, the immortal swordsman continues his endless journey through time, forever burdened by his healing flesh and unyielding ghosts.