Akira's study was quiet, but the air was thick with the tension of sharp planning.
On the desk, a detailed map of the Kanto region was spread out, and Akira's finger was pointing to a spot deep in the mountains on the outskirts of Tokyo, a place not marked on the map.
"Here. Based on Tsubaki's memories, this is the place. It's where a retired cultivator who uses Flower Breathing and took her in long ago lives in seclusion."
Akira picked up a brush and drew a red circle at that point.
"Kanao, Okita, Ushiwaka. You three are going here tonight."
"A cultivator... They're like gatekeepers who teach the basics of Breathing and send people to the Final Selection."
Ushiwakamaru examined the map closely, stroking his chin.
"Right. The Demon Slayer Corps is a closed organization. No matter how skilled you are, it's hard to even get qualification for the Final Selection without a recommendation from a cultivator. You go and obtain that qualification."
Akira took out three talismans with a faint fox flame shimmering from his pocket. They were recognition-impairing and suggestion talismans made by Tamamo.
"Stick these on the threshold of the cultivator's house, or secretly on his body. Then, Tamamo's spell will activate and cast a powerful suggestion. He'll recognize you as disciples he has trained for a long time."
"Heh~ Tamamo-san's spells are so convenient. No need to spill blood by fighting unnecessarily, very smart!"
Okita received the talismans with her characteristic playful smile.
"Remember. The goal is solely the recommendation and joining the Demon Slayer Corps. Don't do anything strange. Especially you, Okita, you're secretly clumsy, so be careful."
"Aw, Master, really! I have common sense too!"
"We'll be back... Father."
Kanao nodded with a determined expression. Her eyes were already those of a general heading to the battlefield. The three briefly bowed to Akira and silently disappeared into the darkness.
A few days later, in the deepest part of the underground laboratory of Akatsuki Trading Company.
In the cold air, Akira was examining his blood sample under a microscope.
The movement of cells visible through the lens was wondrous itself. Constantly dividing and fusing, golden and blue spirals greedily swallowing surrounding energy.
It was not a simple biological structure. Interpreting it in Fate terms, it was a complete material where divinity and demonic nature fused.
After researching with Tamamo and Shuten, the conclusion reached.
"The analysis is complete. Theoretically... injecting my blood rewrites the target's genes at a fundamental level, forcibly blooming their potential. Additionally, by connecting a path with me, it grants sun resistance. Similar to Muzan, but on a different level."
Akira filled a thick syringe with his red blood. The crimson-black liquid emitted a fierce yet enchanting light.
In the center of the laboratory, Tsubaki was kneeling. Her lips were dry from tension, but her gaze was unwavering.
"Are you ready, Tsubaki. This is a point of no return."
"Yes, Master. If I can become your sword, I don't mind becoming an evil demon."
Tsubaki's answer was firm.
Akira without hesitation plunged the syringe needle into Tsubaki's white neck. The piston was pushed, and the blood of the perfect being spread through her carotid artery throughout her body.
Crack! Crunch!
"Guh...! Gyaaaaah!!"
Upon injection, Tsubaki's body arched like a bow. An unbearable scream burst from her mouth.
It was pain as if boiling lead was being poured into her blood vessels.
The sound of destruction, as if all bones in her body were being ground in a mixer, echoed through the laboratory.
If it were ordinary demonification, the mutation would occur slowly over days, but due to Akira's powerful blood, it was compressed and progressed in mere seconds.
Muzan's blood takes longer for stronger individuals to adapt and become demons. But Akira's blood shortens that time, at the cost of immense pain following.
Squelch! Tear!
The white yukata Tsubaki was wearing couldn't withstand the expanding muscles and energy from within and tore in various places.
"Hah... hah... ugh...!"
Her skin turned pale, and red vines crawled up like snakes. The muscles on her back and shoulders developed abnormally, and her slender body was instantly reconstructed into the form of a weapon optimized for slaughter.
Her physique remained similar to before, but her height increased, muscles multiplied and compressed.
Finally, when she opened her eyes. Instead of human pupils, vertically slitted pupils burning red were there.
"Master... my body... it's hot...."
Tsubaki looked down at her hands. Her nails had grown long and black, shining sharply like daggers.
She unconsciously drew the Nichirin Blade at her waist.
Clang!
The moment the sword was drawn, the blade turned crimson-black and emitted a sinister demonic aura.
"This is... my power...?"
Tsubaki lightly swung the sword towards the air. Instinctively, she used her Blood Demon Art.
"Blood Demon Art: Crimson Flower Blaze!"
Rumble!
It wasn't a simple slash. Following her sword's trajectory, the hard concrete floor of the laboratory cracked, and from the gaps, dozens, hundreds of crimson camellia vines burst forth.
The vines wrapped around and crushed the laboratory equipment like living snakes, and red pollen scattered from the blooming camellias.
"This pollen... it's a neurotoxin."
Akira sniffed and muttered. The steel experiment table touched by the pollen was corroding and melting.
"Yes, I can feel it. I can bloom, kill, and poison at will."
Tsubaki trembled. A realm she couldn't reach even after swinging thousands of times as a human. She had surpassed it with a single mutation. She now possessed the clear martial power of an Upper Moon.
"Thanks to you, Master. Truly, I am grateful for this grace!"
"I-Impossible...."
Watching the scene from the door crack, Mukago and Kumohime were captured by fear and awe.
Just minutes ago, Tsubaki was human, but now she had become a monstrous being powerful enough to treat them like insects.
The quality of the demonic aura emanating was different.
"That presence... stronger than Rui. No, even if all Lower Moons of the Twelve Kizuki attacked together, they couldn't win...."
Kumohime muttered, trembling. At the same time, intense jealousy and a sense of crisis overwhelmed them.
'If this continues, we'll be discarded. Master only keeps the strong by his side. If we fall behind Tsubaki, I'll become trash again!'
The two demons rushed into the laboratory as if promised.
"Master!! Please, us too!"
"Give us that blood too! I want to become stronger too! I don't want to lose to Tsubaki!"
Mukago and Kumohime grabbed Akira's trouser legs and pleaded. Their demon instincts craved Akira's blood.
Akira looked down at them for a moment.
'If I inject my blood into demons who were originally demons... what kind of reaction will occur?'
It was worth experimenting.
"Fine. Accept it if you can handle it."
Akira divided the remaining blood into two syringes and without hesitation plunged them directly into their hearts.
"Gyaaaaaah!!!"
A scream far more terrible than Tsubaki's, who was human, burst out.
The rejection and fusion reactions caused by demon cells already present clashing with the cells of the perfect being were pain that literally tore the body apart.
But at the end of that pain, a sweet fruit awaited.
The first to change was Kumohime.
Eight spider legs sprouted from her back. They resembled spider-like spider legs in shape.
Clang! Shing!
With a metallic noise, crimson threads spewed from her body.
"T-This is...!"
Kumohime waved her hand, and the steel threads sliced through the thick iron plates of the laboratory wall like cutting tofu.
"Blood Demon Art: Crimson Spider Hell... The Blood Demon Art Rui used, no, even harder and sharper! My threads... have become stronger than steel!"
Kumohime was entranced, watching the red threads dancing at her fingertips. It wasn't a borrowed ability from Rui, but her own power far surpassing Rui.
Her Blood Demon Art was borrowed from Rui. Is that why? She became able to use the fundamental Blood Demon Art of Rui itself.
And next to her, Mukago's change was more peculiar.
Whoosh~
The temperature in the laboratory rapidly dropped below freezing. White breath like frost spewed from Mukago's mouth.
"Cold... no, refreshing...."
Mukago dazedly stretched out her hand, and the moisture in the air froze, blooming beautiful but deadly ice flowers.
"Blood Demon Art: Crystal Dance."
She flicked her finger, and the ice flowers shattered into thousands of fine ice needles, sweeping forward.
"This is similar to Doma's technique."
Akira muttered, unable to hide his surprise.
Mukago, who only knew how to run away, a coward, had evolved into a powerful cryomancer manipulating ice to create illusions and freeze opponents.
The demonic aura emitted by the three demons filled the laboratory. Each had reached the level of an Upper Moon.
'This... exceeds expectations.'
Akira looked down at his hand.
It was just a few drops of blood. That alone had evolved them into strategic weapon-level beings in an instant.
This was a power even Muzan couldn't easily perform. If Muzan gives too much blood, the demon collapses and dies, but Akira's blood contains the adaptability of the perfect being, leading the target to evolve to the limit without collapsing.
"Master! My body... feels light as a feather!"
"With this power... I feel like I can do anything!"
The three demons, drunk on overflowing power, looked at each other and trembled.
Akira calmly calculated in his mind.
'My blood is a kind of limiter release and evolution catalyst. Those who receive my blood, like my Servants, can probably be controlled, but too many would be troublesome. I, or a mutation like Nezuko, is also possible? And if overdone, like Muzan, it could cause the opponent's cells to collapse.'
A satisfied smile spread across his lips.
"Excellent. You three, now I can call you my elite guard without shame."
"Thank you, Master!!"
The three demons knelt before Akira simultaneously.
The king of demons.
A new king of demons had been born.
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