Cherreads

Crossover Anime: Starting with Zanpakuto from Demon Slayer

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Synopsis
Nanajūhachi Asuka, a soul from the 78th district of Rukongai, is cast into the world of Demon Slayer as a disposable experiment. Lacking a "system" or "cheat-codes," he relies solely on his raw Reiryoku (spiritual power) and the survival instincts of a street dog. Asuka is taken in by Tetsushin Arisaki, mastering Wind Breathing alongside his peer, Suzune. This peace is shattered when Lower Rank Two, Rokuro, massacres their home. Master Arisaki sacrifices himself, triggering the awakening of Asuka’s unique ability: Nugata—the power to devour demon essence and convert it into spiritual energy. Driven by cold vengeance, Asuka joins the Demon Slayer Corps. His presence at Mount Natagumo changes the tide, as his "serrated" strikes—infused with spiritual pressure—permanently stall demon regeneration. This "new variable" catches the attention of Muzan Kibutsuji, who begins purging the Lower Ranks to prepare for this emerging threat. Through training at the Butterfly Estate and sparring with the Mist Hashira, Muichiro Tokito, Asuka realizes a vital truth: traditional Wind Breathing is a "shoe that doesn't fit" his spiritual nature. He begins the journey to transcend established styles, seeking to forge an Original Breath that bridges the gap between a Soul Society ghost and a mortal swordsman.
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Chapter 1 - The Wild Dog of Rukongai

"Hey, kid! Get up! You'll die like that!"

Forcing his heavy eyelids open, Asuka—clutching a battered longsword—warily raised his head and looked toward the towering figure before him.

It was a burly old man carrying a bamboo basket. His bald head was topped with an enormous straw hat that blocked out the falling clumps of snow from above.

He wore a cotton coat that wasn't particularly thick; straw stuffing could be seen poking out from inside. Draped over it was a tattered straw cloak, now piled with snow, full of gaps where the cold wind clearly seeped through…

But compared to Asuka—curled up against a wall in a straw mat, his limbs bluish-purple from the cold—it looked positively warm.

For a brief moment, greed flashed through Asuka's eyes.

He wondered whether he should knock the old man out and steal his clothes… or press his knife to the man's throat and force him to get some food…

But he abandoned the thought.

It was simply too cold—so cold that his hands and feet had already gone numb. He wanted to speak, but no sound came out. He wanted to move, but he had no strength left.

Maybe the old man was right. Maybe he really was going to die…

If he was already dying, what was the point of doing any of that?

The old man frowned as he looked at Asuka's hostile gaze and his lips, frozen purple from the cold.

This kid had already been here for four days…

He wasn't the type to play the good Samaritan, but with the snowstorm showing no sign of ending, simply watching a life fade away before his eyes—well, even the Buddha would be displeased by that.

After a moment's thought, the old man bent down to pick up the scrawny boy. But despite his weakness, Asuka suddenly twitched.

That posture—unable to even support himself, yet still gripping his longsword tightly—made the old man pause in surprise. He quickly said, "Don't overthink it. I just don't want you dying in front of my house."

With that, ignoring Asuka's still-wary and unfocused gaze, he scooped the half-conscious boy into his arms and carried him step by step toward his shabby little courtyard.

When Asuka regained consciousness again, he found himself lying inside a crude mud-brick house.

Firewood crackled in the hearth, the warmth seeping into his body and making his blood feel alive again.

He licked his lips, catching a faint hint of rice aroma. Only then did he notice an empty bowl of porridge sitting on the small wooden table beside his bed.

'That old man… saved me?' Asuka could hardly believe it. The next moment, he jolted upright.

"My sword!"

"On the cabinet."

On the other side of the mud house, the bald old man was leaning against a wooden rack, his face stiff as he sorted winter ling grass from his bamboo basket.

Hearing Asuka move, he didn't even look up—only tapped the surface of the cabinet with the small knife in his hand.

"I don't get it. You're a brat who can't even feed himself—what do you need that broken blade for?" the old man said irritably, shooting Asuka a glance before returning to his herbs.

Asuka didn't respond. He rolled off the bed, staggered over to the cabinet, and pulled the jet-black longsword—its sheath chipped and worn—into his arms.

Seeing that his sword was unharmed, he let out a breath of relief, then nervously looked back at the old man.

After a moment of thought, he bowed deeply and silently.

"..."

The old man's face remained stern as he spoke coldly. "Get back in bed. You just ate something. I'll give you some medicinal soup later. Once you recover, get lost."

Hearing this, Asuka showed no dissatisfaction. He obediently did as told, wrapping both himself and the longsword tightly, cherishing every scrap of hard-won warmth.

His name was Nanajūhachi Asuka.

His past was already blurry in his memory. He only remembered that he wasn't originally from this world—he was a wandering soul from Rukongai.

Rukongai was the dwelling place of those in the Soul Society who had yet to pass on. From District One to District Eighty, the further out you went, the worse the security, environment, and resources became…

Asuka had been captured in Rukongai and sold to a bespectacled man who looked refined on the surface. Through some kind of twisted experiment, the man had thrown him into this place, turning him into a being of flesh and blood.

Three months had passed. These three months were harder to endure than three years in Rukongai.

He had fought stray dogs on the streets for food, snatched valuables from well-dressed townsfolk, and even used this very longsword—brought with him to this world—to fight vicious street thugs. Only by doing so had he survived until now.

But this winter was truly too cold. At last, he couldn't hold on anymore.

'I wonder… if I die here, will I go back to Rukongai?' Asuka thought. 'District Seventy-Eight is awful too… but at least it's not this cold…'

Unconsciously, he tugged the blanket tighter around himself.

Clap, clap. The old man brushed the dust from his clothes after finishing with the herbs. After putting the bamboo basket away, he moved over to the hearth and rubbed his not-so-warm hands in front of the heat.

"Kid. What's your name?"

"... Nanajūhachi Asuka." (Seventy-Eight)

"What kind of lousy name is that? What was your father called?"

"...I don't have a father."

Staring at the ceiling, Asuka replied indifferently. "I was born in District Seventy-Eight, Inutsuri, so my surname is Seventy-Eight."

"...District Seventy-Eight? Where's that supposed to be?" The old man didn't press further, casually asking as he began rolling a crude cigarette from cheap tobacco. "Doesn't sound like a name from around here. You from overseas?"

"Mm… who knows…" Asuka didn't answer directly.

District Seventy-Eight was one of the most lawless areas of Rukongai. Food and water were monopolized, bandit groups ran rampant, and every day was spent in fear.

But he didn't want to tell the old man any of that. He hated looking like a sniveling weakling.

Time passed in an oddly tense atmosphere. The old man never truly chased Asuka away, allowing him to stay.

A few days later, Asuka's body had fully recovered. Still, he chose not to leave. Instead, he silently helped the old man clean the house, chop firewood, tend the fire, and carefully watched how the old man sorted winter ling grass, learning by imitation.

Thus, the old and the young spent the winter together in this strange partnership.

Several weeks later, Asuka was home alone organizing the medicine rack. Yet even as the sun dipped westward, the old man had not returned from the dense forest.

Growing worried, Asuka strapped his longsword to his back and asked the neighbors if they had seen the old man. Their answers matched what Asuka already knew—the old man had gone into the forest to gather herbs and hadn't come back.

His unease deepened.

"Tch… old man… don't go dying out there…"

Night fell, and still there was no sign of him. Unable to wait any longer, Asuka decided to follow the direction the old man usually took and search for him.

The winter night wind carried countless icy shards that battered against the thin cotton coat the old man had given him, cold enough to pierce the bone.

Thick snow piled high beside the towering trees that blotted out the sky, making every step painfully difficult.

Asuka trudged through snow that reached his calves, stumbling as icy grains slipped down his pant legs into his shoes, melting and refreezing against his thin socks. It was miserable—but he didn't care.

"Old man! Old man, where are you?!"

He tried to find footprints in the snow, but after a full day of snowfall, all traces had been buried. With no choice, he raised his voice, letting it echo through the empty forest.

The deeper he went, the stronger a sense of dread wrapped around him—like something ahead was pressing down on his chest, stealing his breath.

He had faced brutal thugs, fought the most food-obsessed stray dogs, even escaped a bear's jaws—but none of that felt like this.

If he had to describe it…

It felt like that vague memory from his past—the bespectacled monster who had subjected him to cruel experiments… that same suffocating sense of discomfort.

Calling out as he moved forward, Asuka suddenly froze, his nose twitching sharply.

"The smell of blood…"

Having grown up amid struggle and plunder in Rukongai, this scent was as familiar to him as air itself. He couldn't be wrong!

Had something happened to the old man?!

A jolt like lightning shot down Asuka's spine. He lunged toward the source of the scent, scrambling forward without regard for snow flooding into his coat or branches slicing his cheeks.

Rounding several thick, ancient trees, and with the help of moonlight reflecting off the snow, he finally saw everything clearly.

The bald old man with the bamboo basket lay sprawled on his back in a pool of blood, his body twisted at an unnatural angle!

The snow was stained red in great swathes. Dark crimson liquid had even frozen into bloody ice crystals on the surrounding bushes—a horrifying sight.

A massive gash tore open the old man's neck, exposing his windpipe and jagged bone fragments to the air. His unfocused eyes stared blankly at the sky, filled with terror and shock.

"Old man!" Asuka's voice trembled, though he didn't realize it himself.

Damn it—was it a bear? Or something else? He should've gone into the mountains with him!

The gruesome scene made his stomach churn violently, a powerful urge to vomit rising in his throat.

He had seen people starve to death, die of illness, even hang themselves—but never anything this horrific. Panic and grief warred in his chest.

Not just these past few months—counting all the years since he'd been born in Rukongai—he had rarely met someone like this old man. Someone who spoke harshly, yet genuinely cared. A true 'good person.'

To be cast into this world and receive such a small warmth… how lucky that had been…

And now it was gone. Just like that. He hadn't even learned the old man's name. He hadn't even said thank you.

But before the immense sorrow could fully drown him, that powerful sense of unease suddenly exploded beside him!

"Heh heh… there's another fresh little one…"