TV-Series
Description
Eiku Shizuma is a supporting antagonist and an early member of the Itto-ryu sword school in the narrative. He is a swordsman who, like the protagonist Manji, has been made immortal through the implantation of sacred blood worms known as kessen-chu. He received this gift from the mysterious nun Yaobikuni during the Muromachi period, which means he has lived for approximately two hundred years by the time he encounters the main characters. Outwardly, he often wears the traditional straw basket hat of a komuso monk, though his true nature is far from that of a peaceful priest.

Before his long un-life, Shizuma was a samurai who served a lord during the Warring States period. He and his comrades were fiercely loyal, sacrificing everything for their cause. However, after witnessing the death of everyone he fought beside and realizing the futility of their struggles, he became disillusioned with human ambition and loyalty. This traumatic past forged a deeply nihilistic and pessimistic worldview. He came to see life as utterly meaningless, believing that people are born like worms and die like worms, and that all their endeavors eventually crumble to nothing. Centuries of watching his wives, children, and friends grow old and die while he remained unchanged left him profoundly weary, and he describes his immortality as a cruel existence.

Shizuma is driven by a desire for power and a search for companionship among those who share his condition. He views the young and ambitious leader of the Itto-ryu, Kagehisa Anotsu, as an unworthy holder of power, describing his goals as an impossible dream. His primary motivation in the story is to recruit Manji as an ally to overthrow Anotsu and take control of the Itto-ryu, believing that their partnership as fellow immortals would transcend the concerns of mortal men. When Manji refuses this proposal, Shizuma resorts to brutal tactics, such as kidnapping Manji's charge, a young girl named Rin Asano, in an attempt to force a confrontation.

He serves as the first immortal antagonist that Manji faces, acting as a dark mirror to the protagonist. Where Manji seeks to use his cursed immortality to atone for past sins by killing one thousand evil men, Shizuma has succumbed to the ennui and moral decay that centuries of invincibility can bring. His role in the story is to challenge the value of eternal life and to present a vision of what Manji could become if he loses his sense of purpose. Throughout his brief but memorable appearance, he tempts Rin with the offer of sharing his blood worms, seeing in her a potential new companion, though this is as much an act of cruelty as it is an offer.

As a member of the Itto-ryu, Shizuma is a figure of some status and seniority, being one of the few members who witnessed Kagehisa Anotsu's childhood. He has no significant allies, as his real goal is personal power and he seeks to use others for his own ends. His key relationships are antagonistic: with Manji, who ultimately rejects and destroys him; with Rin, whom he uses as a hostage; and with Anotsu, whose organization he secretly plans to usurp.

Shizuma possesses formidable abilities, honed over centuries of combat. It is said he has cut down over one thousand people on the battlefield, far surpassing Manji's infamous tally of one hundred. His fighting style has been fundamentally altered by his immortality. He does not fight like a normal human, showing no fear of pain or attempting to dodge lethal attacks, as he has grown accustomed to his body simply healing itself. This reliance on regeneration has, however, allowed his swordsmanship to become somewhat eroded and undisciplined over time.

His most notable trait is his use of a specialized poison. He coats both his saber and dagger, which he collectively names Inoue Shinkai Kosatsu, or Wormkiller, with a toxin called kessen-satsu. This poison is specifically lethal to the blood worms that grant immortality, effectively canceling out an immortal's regenerative abilities and making them vulnerable to permanent death. In his final confrontation with Manji, the poison proves to be a significant threat.

In the end, Eiku Shizuma is killed by Manji, who impales him with his own poisoned sword, a direct cause of death being the destruction caused by the toxin which overwhelms his blood worms’ ability to repair the damage. However, it is heavily implied that Shizuma allowed this fatal blow to land. When asked why he did not avoid the attack, he leaves a final will, expressing his exhaustion with existence: Living as an insect is tiring even to revive. He then provides one last piece of information concerning Anotsu's movements before passing away. His grave is later built by Rin, the girl he had kidnapped.
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