Infinity Castle, now under Akira's control instead of Muzan's.
Whenever Nakime strummed her biwa, it immediately connected to anywhere—whether the Demon Slayer Corps headquarters' Butterfly Mansion, training grounds, or even Akira's bedroom.
As night deepened, Kanao and Okita, who were secretly active within the Demon Slayer Corps, along with Ushiwakamaru, teleported to Infinity Castle via Nakime's biwa.
Of course, in their absence, elaborate clones created by Tamamo's spells remained, pretending to sleep and perfectly deceiving the Demon Slayer Corps' surveillance.
"Master~! I missed you today too!"
In the banquet hall of the Heavenly Palace, the highest level of Infinity Castle, Ushiwakamaru ran and hugged Akira like a wagging-tailed puppy.
"Everyone's here. How was training today?"
Akira asked while stroking Kanao's head.
Kanao silently blushed and leaned against his shoulder, and Okita sat next to Akira holding dango. This place was their only sanctuary in the battlefield and their secret paradise.
But the rest was brief; the instincts of warriors wouldn't leave them idle.
In the grand training grounds of Infinity Castle's lower levels, a spar beyond common sense was taking place.
The sharp clang of swords echoed through the air.
The female-form Kokushibo stepped back, sweating. Her six eyes widened in shock.
"...Fast."
Before her stood Okita Souji, wearing a Shinsengumi haori.
"Oh my? Moon Breathing is quite tricky. Swords flying from all directions."
Okita smiled brightly, but the Shukuchi and Mumyo Sandan-zuki she had just shown were so swift that even Kokushibo's dynamic vision could barely read them.
That speed, as if transcending space, was a different kind of terror from Yoriichi's slashes.
"I'm here too! Moon-sama!"
From above, Ushiwakamaru descended, swinging her sword.
Her movements seemed to ignore gravity.
True to the legend of the eight-foot leap, she freely changed direction as if there were invisible footholds in mid-air, aiming for Kokushibo's blind spots.
"Moon Breathing, Ninth Form: Waning Moons – Layers."
Kokushibo unleashed a wide-area slash with all her might, but the two Servants slipped through the gaps and aimed their swords at her neck.
"...Defeat."
Kokushibo sheathed her sword and let out a deep sigh.
This was the second spar. After one battle in her familiar male form, she was defeated again in female form.
But her face was not filled with despair, but with overwhelming joy.
'Yoriichi wasn't... the only god.'
The wall of inferiority that had oppressed her for hundreds of years crumbled slightly.
The world was vast, and unknown strong beings existed. Yoriichi was not an unreachable sun, but merely one among many monsters.
"I can... still grow stronger."
Kokushibo clenched her fist. Those stronger than her were now by her side as comrades.
The hope that, by sparring and learning from them, she might one day reach that distant realm thrilled her.
"Enough, come back already?"
"Have a snack first."
"Really, Master, now you're being eyed by a hundreds-year-old grandfather too."
"That's right~ What sin did you commit in your past life, Master?"
"Indeed."
Watching from afar, Akira frowned with a firm attitude of disliking the female form, and Benienma naturally handed him a rice ball.
Kiyohime and Tamamo sighed, lamenting that now even a hundreds-year-old man was after him, and Akira himself naturally disliked it too.
It was the swordsman's peculiar competitive spirit, forged from centuries of inferiority.
"Anyway, Michikatsu. These are the disciples you'll teach from today."
At Akira's words, Kokushibo looked at the two girls with surprise.
"Disciples... you say?"
"Yes. You'll learn more by teaching than training alone."
Akira pushed Shinobu forward.
"Pay special attention to Shinobu. Her Nichirin Sword color."
Shinobu drew the sword from her waist. One of the Nichirin Swords sent by Kanao, which Shinobu had wielded. The blade had a faint lavender hue.
"...!!"
Kokushibo's eyes narrowed.
"This color... it's suitable for Moon Breathing. Rare..."
"Right. Shinobu lacked physical strength as a human, relying only on stabbing and poison. But now, she's become a demon after receiving my blood."
Akira placed his hand on Shinobu's shoulder.
"The strength issue is solved. With her demon physical abilities, she's now a swordsman who can slash. But having only stabbed all her life, she lacks the feel for slashing. Probably because Flower and Water Breathing aren't very suitable for her. You awaken that sense and teach her Moon Breathing."
"And that one?"
Kokushibo looked at Kanao standing behind.
"Kanao has genius-level dynamic vision and fast learning ability. But Moon Breathing is erratic and difficult. With her current basics, she can't handle those irregular slashes yet. Teach her fundamentals, but have her observe Shinobu's training."
Akira brought Kanao because he believed in her talent and wanted her to learn from Kokushibo, who had lived for centuries as a Breathing swordsman, to gain experience.
It would be good if she learned Moon Breathing, but he didn't have high expectations.
From that day, Shinobu's hellish training began. Her opponent was Kokushibo.
"Too honest, Shinobu!"
Clang!
Kokushibo lightly parried Shinobu's sword. Habit was a scary thing. At critical moments, she unconsciously extended her sword in a stabbing motion.
"You've dedicated your life to stabbing. So your sword trajectory is linear. Now that you're a demon, don't waste that strength."
Kokushibo demonstrated.
"Moon Breathing, Second Form: Pearl Flower Moongazing."
It looked like a simple series of slashes, but around the trajectory, numerous crescent-shaped slashes bloomed irregularly.
"The core of Moon Breathing is chaos. As you swing the sword, visualize the derivative slashes around it. Your sword is ready to accept that chaos."
"...Yes!"
Shinobu gritted her teeth. After becoming a demon, her physical strength had exploded. Before, she couldn't even push a rock, but now she could crush rocks bare-handed. She adjusted her grip on the sword.
'This Breathing technique suits me.... I understand what kind of slash fits me, who has mainly stabbed.'
Shinobu charged again. This time, it wasn't a stab. Using the snap of her wrist, she swung the sword wide.
Whoosh!
But the unfamiliar trajectory only cut through the air.
"No. Don't try with just strength. Recall the technique I taught you. Simply put, trust your flexibility. The Flower Breathing you learned is a gentle slash. You must add the erratic and wide-ranging nature of Moon Breathing to that gentleness."
Kokushibo approached from behind and corrected Shinobu's posture.
"A woman's body is soft. Use the elasticity of your back and waist, not just your arms. Swing it like a whip, but slash with weight at the end."
Shinobu repeated Kokushibo's advice and adjusted her breathing. The speed of her specialty, Insect Breathing, and the demon's physical strength. She sublimated the technique Kokushibo taught with flexibility.
Shinobu focused her breathing. Filling her lungs with air, she felt Akira's blood flowing through her veins. Strength was sufficient. Technique was sufficient. What she needed was the image of slashing.
'I'm not... a bug that stabs with poison. Now... I'm a demon who severs necks.'
Shinobu kicked off the ground and leaped. Her movements were elegant as if dancing, but the speed of her sword swing tore through the sound.
Moon Breathing, Seventh Form: Mirror of Misfortune – Moonlit.
Crash!
Shinobu's sword spread out like a fan, cleaving the space. It wasn't a simple slash. Following the trajectory she swung, numerous crescent-shaped blades irregularly sprang out, turning training dummies to dust. A strike combining the speed of stabbing with the destructive power of slashing.
"...Success."
Kokushibo nodded. Shinobu looked at her own hand. The weighty feel of being able to sever a neck. It was the sensation she had longed for all her life.
"Thank you... Master."
Tears welled in Shinobu's eyes. Now she had become a complete swordsman.
Meanwhile, in the corner of the training grounds, Kanao watched with clenched fists. Shinobu learning Moon Breathing was marvelous. At the same time, anxiety arose from the fact that she couldn't follow that sword yet.
Kokushibo called out to such Kanao.
"Kanao. You're still lacking to use Moon Breathing. But you have a weapon more outstanding than anyone."
Kokushibo pointed to her own eyes.
"Your eyes. You were watching Shinobu's movements and my guidance without missing a single detail."
Kanao nodded. Her eyes had been recording Shinobu's muscle movements, breathing changes, and Kokushibo's sword strikes as if collecting data throughout the training.
"Moon Breathing is difficult. The size and length of the slashes change arbitrarily. But with your eyes, you can find the rule within that irregularity."
Kokushibo gave Kanao an assignment.
"Don't mimic techniques for now. Instead, watch Shinobu and my spar and predict where the next slash will come from. When your dynamic vision fully reads the moon's trajectory, you'll realize something beyond Flower Breathing."
Kokushibo looked into Kanao's eyes.
"Your eyes are a treasure. Engrave Shinobu's movements, my muscle contractions, the flow of air... all of it. You have a talent that my past Tsuguko didn't have."
"...Yes, I understand."
Kanao nodded.
Watching all this from afar, Akira smiled with satisfaction.
"Kokushibo, she's quite good at being a teacher, huh?"
Ushiwakamaru, standing beside him, laughed while tapping her shoulder with her scabbard.
"Having been blocked by the wall called Yoriichi herself, she understands her disciples' hearts better. You have a good teacher now."
"Right. Shinobu has now become a complete entity with attack power, and Kanao is preparing to explode her potential."
Akira emptied his wine glass and muttered.
"Muzan. Soon, I'll make you painfully realize that this harem knight order I've created is far stronger than the Twelve Kizuki you made."
"Calling it a harem knight order sounds a bit shabby, Master."
"Is that so? My naming sense is a bit lacking."
Okita naturally interjected from the side.
Kanao trained by predicting slashes during sparring with Kokushibo rather than directly learning Breathing.
Later, as time passed and training ended, Shinobu and Kanao, soaked in sweat, sat on the floor to rest. Kanae brought towels and wiped their sweat.
"You worked hard, Shinobu. And Kanao. Both of you are amazing."
"Sister... now I can learn a slashing Breathing that suits me."
Shinobu said, holding Kanae's hand. The sibling bond remained unchanged even after becoming demons.
"Hehe, I'm glad too. Even though becoming a demon made slashing no problem, it didn't mesh well with Flower Breathing, which was disappointing. It's truly a relief."
Kanae hugged her sister tightly. Watching this, Kokushibo felt a strange emotion.
'Siblings... sisters...'
Her relationship with Yoriichi had ended in ruin.
But these sisters supported each other and grew stronger together.
'Is this... the bond Yoriichi spoke of? Complicated. Even though the younger sister is more talented than the first-born, it's so different.'
Kokushibo felt a bitter yet complex emotion.
"A good picture."
Akira approached and looked down at them.
"Shinobu has become the core of attack, and Kanao is nurturing her potential. Kanae, you can't fall behind your sisters, can you?"
"Oh my, Master, really. I'm their sister and your wife. The type of strength is different."
Kanae smiled leisurely and winked at Akira.
"I suppose. Everyone, keep striving. There's nothing bad about being strong. By the way, I guess I have no talent for Moon Breathing either. Well, not being able to use Breathing isn't a problem."
As a perfected being, he couldn't just stay idle, so he tried to learn Breathing.
But he had no talent for Moon Breathing either.
What does talent for Breathing matter? If you're strong without it, that's enough. At the point where he can use the Servants' swordsmanship, he's already a top-tier strong warrior in this world.
"Anyway, in a few months, it'll be time for Gyutaro to come to Yoshiwara. I wonder if he'll come here too."
He thought about how fate would flow from now on. No matter the flow, ultimately, they would control it, so there was no worry.
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