321 Hashira's teachings: Sword Spirit, Releases, Bankai, and ...

The smell of cooked fish lingered around them like a thousand butterflies.

Kai and Shinobu were seated facing each other with the fire to their left. On a rock between them, the cooked salmon was steaming, its flesh charred at the edges.

Shinobu used some makeshift chopsticks to pry the flesh open and took a bite.

"It's hot," Kai warned, seeing her widened eyes. "Let me." He took out another small chunk of the fish, blew over it several times, and then extended it towards her, a gentle smile lingering on his face.

Shinobu observed him for a moment. Suddenly, her hand flashed, taking off the flesh pinched between Kai's chopsticks, and ate it.

Kai couldn't help but laugh.

On their right, there was a little straw hut surrounded by snow. Inside the hut, Nezuko was sleeping soundlessly, curled into a little ball.

Kai made sure that the package was truly sleeping, and then helped himself to a bite, his stomach roaring to devour a beast by itself. With no sign of demonic hunger, Kai blew on another piece and handed it over to the Insect Hashira. This time, she leaned forward and ate it off his chopsticks.

A snail popped to their left, fire crackling, dancing fiercely over the twigs and logs.

In silence they ate, forgetting the worldly troubles and worries. Over their head, the crescent moon shone, showering them with silvery light.

Kai's hand lifted and reached for her face. Taken by surprise, Shinobu stiffened, her faded purple eyes landing on his innocent hazel pupils. Kai's thumb gently landed on the corner of her lips, rubbing away a stray piece of morsel.

Color rose to her face instantly. "You…" she said, furiously scratching her lips. "Don't touch me like that."

"Haha!" Kai's laugh sounded playful, his gaze landing on the sky overhead. Words came naturally to his lips, as he sang, bringing his gaze back on her, his voice ethereal, and weighed with longing and sadness.

"On the mountains the snow sheens white;

Amid the clouds, the moon shines bright.

Today the banquet we attend;

Tomorrow we'll part by the moat end." [1]

Her hand, carrying the chopstick and going towards her mouth, suddenly paused, and Shinobu's pupils trembled. She looked up at him and found Kai looking back at her with the same smile.

A buried sigh escaped her throat. "Why aren't you using the Flower Breathing Style?" she reprimanded, her tone fueled with anger and pain. "Why are you so adamant about creating a new Breathing Style for yourself? It takes months and years to create a brand new Breathing Style. If not for your stubbornness, you would have already become proficient in it."

Even with her reprimanding words, the shock, praise, and pride were easily noticeable. Kai was a monster. Give him a hint, and he could unravel the deepest mysteries by himself. No teacher would have hoped to get a better student than him. And thus, the Insect Hashira hadn't held back, either, pouring knowledge and experience relentlessly into his mind during the last few days.

Kai took a deep breath and shook his head. "It doesn't suit me," he told her. "No Breathing Style currently used by the Demon Slayers, as told by you, suits me. I know I can play it safe by just going along with the process. But is there any adventure in that? Haha! Who am I? The brilliant doctor Arlen, whom even demons couldn't turn. No. I will create my own Breathing Style. And if I failed…"

Kai took a snail out of the fire, used the chopsticks to pinch the flesh out of the shell, and threw it in his mouth. "… Well," he said, his eyes beaming like stars, "then I will just have to start over, right?"

Shinobu gawked at him, her eyes reflecting the majestic appearance of Kai and the gleaming red jewel on his forehead. Suddenly, she burst out with laughter as well. "I have nothing left to teach you regarding the initial Breathing Style, Arlen," she said, looking down. "And it's too soon for you to know more than that. But I think, considering your circumstances, you must know a few details regarding Hashiras and Upper-ranked demons. And you are too humble to ask them from me…"

The last sentence had barely come out as a whisper, buried under her breath. Kai had caught the words, nonetheless. However, he said nothing, keeping quiet. He knew she would tell him by herself. The image that he had created of himself inside her heart had already taken root.

Shinobu sighed. "Now, I will tell you the entire journey of becoming a Hashira," she said, straightening herself up.

Kai put down his chopsticks over the rock and focused his eyes on her lips. The moment words left her mouth, he would imprint them in his mind, Kai thought. "Yes, master," he replied, nodding at her.

Shinobu put a hand over her lips and giggled. "What?" she jested, playfully. "Not calling me by my first name anymore."

"Why?" Kai asked, raising an eyebrow. "You are already missing it, Shinobu?"

Shinobu snorted, but her eyes looked pleased enough. "All potential Demon Slayers start their journeys by learning a Breathing Style," she began, tutoring Kai like a teacher. "Then the candidates undergo a test before finally becoming Demon Slayers. During this selection, examinees must survive for seven days on a mountain top infested with demons with no aid from the outside world.

"The passed candidates are then allowed to select Scarlet Ore for their swords, called Nichirin Swords, forged using Scarlet Crimson Iron Sand. These swords constantly absorb sunlight, making them the only weapon that can permanently kill demons by decapitating them. Nichirin Swords take on a distinct color when first drawn by their owner, which is why they are also referred to as "Color Changing Katanas". Here things become more complicated if one's mastery over their Breathing Style is lacking."

Kai's eyes narrowed to the faintest degree.

"Now what I am going to tell you is confidential even among the Demon Slayers," Shinobu continued, showing her trust in Kai. "Only a select group of Demon Slayers, who excel in their fields, undergoing rigorous training, and achieving significant results under Hashiras, may know it. Because knowing this before becoming qualified for it is useless. I, Insect Hashira, Shinobu Kocho, choose to divulge this information to my Tsuguko, Dr. Arlen, now."

'What's going on?' Kai thought, sensing the seriousness of the topic. 'Why the need for such words? Wait a minute! Is it related to…'

Kai's thoughts were on point.

Shinobu looked extremely solemn as she began her teachings. "All living beings in the world consist of two bodies," she told him. "The first is physical, and the second is spiritual. Physical bodies can be trained using various methods, surpassing known humane realms and limits. But the Spiritual Bodies remain unchanged throughout one's life.

"Now, a Spiritual Body has two components. Spiritual Power, called Reiryoku. It is a power aligned with the spiritual sensitivity and willpower of the user. The other one is Spiritual Pressure, called Reiatsu. It is the physical pressure that a person's Reiryoku, or the Spiritual Power, creates when released."

Kai's heart was already thumping wildly. He forced himself to calm down, regaining his composure. 'This is exactly like the concepts of Bleach,' Kai thought, recalling the things told to him by Item-M. 'So this is the power of Verse Fusion. Magnificent!'

"A Demon Slayer's journey is to tap into one's Spiritual Body, awakening both Reiryoku and Reiatsu little by little," Shinobu continued. "That's why Breathing Styles are necessary to become Demon Slayers. Not only do they allow the Physical Body to transcend the humane limits but also stimulate the Spiritual Body, allowing the Demon Slayers to sense its presence. This stimulation is paramount… for the birth of the Sword Spirit."

Kai's pupils trembled. "Sword Spirit?!" he asked but thought "Zanpakuto Spirit" inwardly.

Shinobu nodded, a stray tongue of fire trying to lick the rock between them. "When a Demon Slayer, who has a firm grasp on the Breathing Style, gets the Nichirin Sword," she said, pointing at her sword, "the sword forcefully draws out the Reiryoku, changing color. This change of color depends on the color of a Demon Slayer's Reiatsu. And this forceful drawing out of Reiryoku and changing of the sword's color is called Spiritual Awakening.

"When the Spiritual Body awakens, inside the subconscious world of a Demon Slayer, also called the Inner World, the Sword Spirit takes form. Sword Spirits are a part of Demon Slayers' souls, and their appearances and abilities reflect this; as such, they also share their master's resolve. A Sword Spirit's power is separate from that of its owner, and when a Demon Slayer draws on this power besides their own, they will become even stronger. Some say that a Sword Spirit is ever present in the Inner World in one form or another, even before the Spiritual Awakening. But this has never been confirmed."

After saying this, Shinobu paused and prepared tea for them.

Kai gazed at the steaming pot they'd got from a village, his mind racing, forming theories after theories. Yet, he was patient enough to know when it was time to advance and when to retreat. He wouldn't dare to show weakness after coming so far with a Hashira.

Shinobu poured tea into two cups and handed one to Kai, their warm hands brushing against their skins like profound ice. The Insect Hashira snatched her hand away, sipped the tea, and took a deep breath.

"The next step on a Demon Slayer's journey is to master the two releases of the Sword," she said, throwing a piece of charcoal at Kai's swishing tail. "Shikai, or Initial Release, is the first release. To activate it, the Demon Slayer needs to learn the name of their Sword Spirit. The Demon Slayer must be able to communicate and harmonize with their Sword Spirit effectively, which requires being able to speak to the spirit within its world. Gaining access to one's Shikai and releasing it for the first time is known as Manifestation.

"The blade gains special abilities by chanting a Release Call. For example, Rengoku's Roar and my Cry. Using the Release Call, followed by the name of the Sword Spirit, activates Shikai. Achievement of the Shikai is a mark of control, and it is a requirement for advancement within the Demon Slayer ranks."

Kai remembered how Rengoku's sword, Kagutsuchi, had already been glowing red-white hot when he unsheathed it. 'So,' he reflected, 'that was his Shikai.'

"Is the second release…" Kai mumbled, remembering the fiery, mountainous pressure and the Flame Hashira's transformation.

"Bankai." Shinobu completed it for him. "It is the final release," she told him. "Sigh! Achieving Bankai is very very very hard, Arlen. One can even say that having Bankai, regardless of the contributions, is a one-way ticket to becoming a Hashira. There are many conditions a Demon Slayer must fulfill to even have a shot at it.

"First, one must have the resolve to do or die, pushing oneself beyond limits. Depending on the amount of training and natural talent, such Demon Slayers can awaken many Demon Slayer Marks over their bodies in life-threatening situations. Second, one must know the Bankai-name of the Sword Spirit. It is an upgraded version of their Shikai-name. This Bankai-name can only be learned by awakening over one Demon Slayer Mark and using the resonance between these marks to evolve the Sword Spirit. The power of Bankai is easily over 5 times greater than Shikai. But if one fails to achieve Bankai, despite resonating the Demon Slayer Marks and evolving their Sword Spirit, then one's life essence will be consumed. This… is the Curse of the Mark."

Kai fell into deep silence, showing a downcast expression. Inwardly, he was roaring in astonishment. 'What the actual fuck?!' He thought, repeating the lesson. 'Shikai is almost the same as the one in Bleach, but the Bankai is entirely different. Damn! No matter what, achieving Shikai and Bankai in this world without the Nichirin Swords sounds impossible. Tch! Huh? Wait a minute…'

"Did you say Bankai's strength is over 5 times greater than Shikai's?" Kai asked, licking his lips. "Then why are the demons still alive? They don't have the Nichirin Swords necessary to awaken their Spiritual Bodies, right?"

Shinobu closed her eyes and sighed. "You are right." She nodded, her smooth fingers clenching the cup. "They neither have the Shikai nor Bankai. But…"

She looked up at him, and Kai could've sworn he saw a trace of fear in her eyes.

Her next words made Kai almost spit out the tea in his mouth.

"… but they have…"

******************

[1] To a Faithless Husband - by Zhuo Wenjun