Yaoshi

Biodata

Power Progression

Background and History

Virus outbreaks

At Yokohama Port, Sabito tracked stolen medicinal ingredients to Yaoshi. Yaoshi incapacitated him with a pink mist and a virus that changed his body, then escaped after naming him “Test Subject Number One” 127 129.

Yaoshi’s evolving viruses caused outbreaks across towns and Demon Slayer Corps outposts. Giyu pursued him across Japan, but Yaoshi repeatedly disguised his movements and left infected victims behind 131 139.

Search for the Blue Spider Lily

After his improved-blood experiments produced subjects who exploded or became mindless, Yaoshi concluded that he needed an exceptional specimen. He also theorized that the Blue Spider Lily bloomed during daylight, burned his research records, and headed to Mount Kumotori disguised as a traveling doctor 133.

At a free clinic, Tanjiro told him that a blue flower called the Azure Sky Illusion Dream grew near his family’s ancestral graves. Yaoshi gave Tanjiro medicine for his father, Tanjuro, while secretly planning to use the family as test subjects 134 138.

After three days near the grave, Yaoshi risked the sun to reach the blooming flowers and ate them. Their power restored his burning body and made him immune to sunlight 138 140.

Capture and death

Tanjuro confronted Yaoshi and repeatedly cut him apart with Hinokami Kagura, but illness and exhaustion left him unconscious. Giyu arrived before Yaoshi could kill him, dismembered the demon, and carried his bound body and severed head to Mount Sagiri 141 142 143.

Muzan invaded Yaoshi’s memories and learned that he had conquered sunlight. Seeking Yaoshi’s cells, he sent his forces to Mount Sagiri, where Tamayo and the Kocho sisters worked on a medicine to turn Yaoshi human 146 147 168.

Yaoshi escaped during the attack on the cabin, but Sabito and Kanae pursued him. Shinobu injected him with medicine made using his own blood; it initially drove him into a berserk transformation. Sabito subsequently broke through his armor and severed his head as the medicine caused his cells to collapse. Yaoshi was completely erased 172 176 177 178.

Appearance

Yaoshi appeared as a handsome, refined young man, often presenting himself as a physician 133 168.

• Glasses: Gold-rimmed, limited-edition glasses that he claimed were made of pure gold 144.
• Clothing: A white, custom-made lab coat 134 168.
• Berserk form: A swollen body covered in blue-purple veins, with more than a dozen thick tentacles ending in fanged mouths 176.

Personality

Yaoshi cultivated a gentle, compassionate doctor’s persona to win trust and extract information. In private, he regarded people as specimens and imagined subjecting the Kamado family to painful experiments 134 138 139.

Proud of his scientific intellect, Yaoshi aspired to surpass Muzan and rule as a god. He was also intensely concerned with cleanliness and resented the dirt and discomfort of hiding on Mount Kumotori 133 135 138.

Despite his loyalty to Muzan in public, Yaoshi feared being consumed for his sunlight-resistant cells and intended to escape both Muzan and the Demon Slayers 145 168.

Abilities & Skills

Medical research and viruses

Yaoshi developed experimental medicines and rapidly evolving viruses, using human subjects to test their effects 127 131 133.

• His pink virus transformed Sabito into a girl and initially drained his strength 127 129.
• A blue virus caused poisoned Corps members to attack people they feared seeing 131.
• His improved-blood experiments failed when subjects exploded or became mindless 133.
• As a physician, he identified toxins in a snakebite and rapidly applied silver needles to the patient’s leg 134.

Poison-based Blood Demon Arts

Yaoshi preferred to attack from a distance with mist, poison, and viruses rather than fight hand-to-hand 142.

• Corrupting Hotbed: Released green poisonous mist that formed writhing, snake-like shapes. Tanjuro’s flaming axe evaporated it 142.
• Epidemic Spread: Weakening Swamp: Turned the ground into a glowing swamp that induced weakness and dizziness. Sabito dispersed its poisonous mist with Twisting Whirlpool 172.
• Virus Theater: Produced fatigue-inducing pink fog and muscle-stiffening poison needles 175.

Regeneration and body manipulation

• Before gaining sunlight immunity, Yaoshi regenerated an arm severed by Sabito 127.
• After eating the Blue Spider Lilies, he reassembled from severed body parts and survived repeated dismemberment by Tanjuro 140 142.
• He grew tentacles for movement and attack, including tentacles carrying corrosive poison 175.
• He formed hard keratinous armor over his neck and later over his body 176 177.
• His regeneration was not enough to prevent the Demon Transformation Medicine from causing irreversible cellular collapse 177.

Equipment and Items

• Medical case and silver needles — Used during his free clinic to treat patients and maintain his doctor’s disguise 134.
• Scalpel — A bloodstained scalpel gave Giyu a scent clue leading toward Tokyo 131.
• Medical records — Documented his experiments at an abandoned hospital; Yaoshi burned them before leaving for Mount Kumotori 133.

Relationships

• Muzan Kibutsuji — Yaoshi’s superior, who valued his intelligence. Yaoshi secretly sought independence from him, while Muzan wanted his sunlight-resistant cells 145 146 168.
• Sabito — Yaoshi’s first named test subject and later one of his captors and pursuers. Sabito ultimately severed his head 127 168 172 177.
• Giyu Tomioka — Pursued Yaoshi across Japan, captured him on Mount Kumotori, and brought him to Mount Sagiri 131 143.
• Tanjiro Kamado — Trusted Yaoshi as a doctor and told him where the blue flowers grew; Yaoshi privately considered him a specimen 134.
• Tanjuro Kamado — Tanjiro’s father, whose frail but unusual body fascinated Yaoshi. Tanjuro later fought him to protect the family 137 141 142.
• Tamayo, Shinobu Kocho, and Kanae Kocho — Used Yaoshi’s blood to develop medicine intended to turn him human. Shinobu injected it during the fight on Mount Sagiri 168 176.

Legacy

Tamayo later used Yaoshi’s blood alongside Giyu’s cells to make a strength-enhancement serum. In an experiment on Sabito, the serum rapidly strengthened his muscles and showed potential for improving Demon Slayer Corps swordsmen’s physical abilities 198.