Demon Slayer : The Cursed One.

Kai's Astral Core didn't form, and even with Lisa's guidance, he failed to master the most basic breathing techniques. 

These techniques, though fundamental, had occasionally helped rare individuals awaken their dormant cores but Kai showed no signs of progress.

Lisa had spent weeks, then months, trying to guide him through the motions. She adjusted his breathing patterns, created a workout to suit his frail constitution, and even tried various meditation methods to center his mind. 

Yet nothing worked.

The Awakening Potion had caused a temporary fever, unusual hair discolouration, and fatigue, but no signs of spiritual energy stirred within him. 

His failure was as clear as the blank space where his Astral Core should have formed.

Lisa never voiced her disappointment, but Kai could see it in her faint frowns, in the way she lingered on her notes for longer than usual, and in the rare moments her sharp green eyes softened when they met his. 

Despite this, she never gave up on his treatments, although her efforts gradually shifted toward maintaining his condition rather than pursuing the impossible.

—--

By the second year, Lisa's health began to deteriorate. At first, the signs were subtle. Her movements became slower, her posture less upright. 

The dark, emerald sheen of her hair began to fade, and strands of silver crept in like frost on a winter morning. She coughed often, her breath rattling in her chest.

Kai had asked her once if she was ill. She had dismissed the question with a wave of her hand and a sharp tone that brooked no further inquiry. 

Lisa had always been meticulous about drawing boundaries, and Kai had learned early on not to cross them.

But her decline was undeniable. By the third year, her condition had worsened significantly. Her once-sharp steps were replaced by unsteady shuffles. Her once-commanding voice became soft and hoarse, and her green eyes dimmed, though their piercing quality remained.

Lisa could barely stand by the time her fourth year with Kai began. She rarely left the house, spending most of her days lying in bed or sitting in the corner of the lab, directing Kai with gestures and short instructions.

Kai had quietly taken over many of the household tasks. He ensured she had food, kept the fire burning, and tended to the remnants of her lab. The medicines Lisa once crafted to aid others now served to ease her own suffering.

Whatever wealth Lisa had possessed had dwindled to almost nothing. Kai noticed the absence of certain materials and rare ingredients in her lab, signs that she had spent it all on her work or something else she never explained. They lived frugally, surviving on what little she had left.

—---

Now, standing before the cracked mirror, Kai began to undo the buttons of his coat. 

The cold air of the room pressed against his skin as he shed his coat, sweater, and shirt, exposing his frail frame to the biting chill.

In the warped glass, his reflection stared back at him—a malnourished boy with pale skin and a gaunt frame. His ribs jutted sharply, his collarbones pronounced. His hair, once raven black, was now streaked with white, a permanent reminder of the Awakening Potion that had failed to awaken anything within him.

His face remained expressionless, but his hands moved to his chest, brushing against the blister-like marks that marred his skin.

The marks spread unevenly across his torso, making his skin look shrivelled and rotting in places. Despite Lisa's treatments, they had never fully disappeared. They burned with a dull, constant ache, a pain he had grown so accustomed to that it was part of him now.

He pressed his fingers lightly against one of the marks, his hollow gaze locked on the mirror. The sharp sting that followed barely registered.

The marks had begun to spread again in the months before Lisa's death. They crawled across his chest like vines, bringing with them a familiar, gnawing pain. He hadn't told Lisa about it. She had enough to deal with.

He had seen the strain in her eyes, the way her hands trembled as she worked in the lab, and the lengths she went to hide her own pain.

—--

A week before her death, Lisa had finally told him the truth about the marks.

They weren't the symptoms of a disease or ailment, but the curse of an ancient noble bloodline—the Ubuyashiki family.

Lisa had explained their origins in her usual detached tone. 

The Ubuyashiki family had existed long before the modern Bastions, even before the Edo period, in a nation that had once stood on the Asian continent. 

The family had been the founders and leaders of the Demon Slayer Corps, a group dedicated to protecting humanity from demons.

But their noble lineage carried a curse.

Every male child born into the Ubuyashiki family suffered from a debilitating condition—a burn-like skin affliction that slowly consumed their bodies. The disease would spread until it covered them entirely, drastically shortening their lifespans.

The male members will die before he reaches thirty, with no exceptions.

Lisa had told him little beyond that. She hadn't explained why the family was cursed or whether it still existed. She hadn't said if he was the last of his bloodline or if there were others like him somewhere in the world.

Kai hadn't pressed her for answers. Lisa's intentions had always been her own, and Kai had long learned that some questions were better left unasked.

Turning away, Kai started putting on his clothes and protecting himself from the cold. 

He didn't dwell on Lisa's revelations, even if they were still weighing heavily and unanswered. Dwelling had never been his style. 

He had been taken aback when Lisa had initially revealed his relationship to the Ubuyashiki family. 

However, the news had not evoked strong feelings in him, such as rage, hope, or a sense of kinship with a family he had never met. Perhaps locating the Ubuyashiki family will result in a remedy. 

However, Lisa had not verified whether they possessed one. They didn't, according to Kai's keen and frequent right instincts. What would happen if they only had a partial solution? 

Would he live a life of suffering and degradation, his body rotting like a rat with a disease? 

He was also unable to deny the notion that Lisa had picked him in order to study his curse in the hopes of healing her own, possibly out of desperation. His failure to construct the core had destroyed her plan of action, if she had had one. 

The room was silent, save for the faint creaks of the house under the weight of snow. As he stared at his reflection, a memory surfaced, ringing clearly in his mind.

Kai's gaze remained fixed on the mirror as he muttered under his breath, "Desire…"

He touched his chest again, his fingers grazing the cursed marks. His voice was low, almost a whisper. "I wonder what mine is. Perhaps it could give me a reason to continue."

Kai wasn't sure what he wanted now that she was gone. Was a longer life like this really worth living? Perhaps it was best to pass away without the increasing discomfort, on his own terms. 

If the Ubuyashikis were still alive, they could wait. Kai didn't want to discover them now. He was reminded of what he already knew by the marks on his body.

He dropped his hand from his chest and looked at the distorted mirror again. There was a small flash of thought somewhere in the nothingness of his hollow eyes, but his face was blank. 

The cool air made Kai's breath mist as he walked around the darkened room. He grabbed his coat and put it back on. Then he took his damaged handgun out of one of its secret inner pouches.

"Thanks," Kai mumbled, holding the rifle loosely in his right hand. The word was almost heard, but its weight, heavy and unsaid, hung in the room. 

A sudden pressure touched his neck as he turned to face the table. A blade pricked him, leaving the smallest trace of blood, as a tiny warmth ran down his skin. 

The silence was broken by a harsh, low voice behind him. "How were you aware of my presence?" 

Kai didn't recoil. His body was eerily motionless, even with the blade placed close to his throat, and his hollow eyes remained focused on the wall in front of him.

As though making a weather-related remark, he answered in a flat, distant voice, "I have good instincts, and I appreciate two things." The blade remained steady, its sharpness icy against his flesh. Behind him, the voice remained quiet, waiting. 

"The first is for letting me get dressed before you try to kill me," Kai added in a serene, almost unconcerned tone. "I wouldn't particularly want to die nude." Then there was a tense, expectant silence.

"And the second one..." Kai moved his hand in a one swift motion, lifting the handgun. 

BANG! BANG! BANG! 

He fired quickly at the metal sheet wall in front of him rather than aiming behind him. His arm was jolted by the recoil as the rounds cracked like thunder. 

Moments after the bullets ripped through the metal sheets, there was a muted thump from outside. Kai, not to be deterred, lowered the revolver. "...For allowing me the opportunity to deal with those fools outside. I spared them previously, but they didn't get the message. I assumed they would at least hold off on sending someone after me for a week, but I guess patience isn't their strong suit." 

For a moment, all was still.

Then a low, rumbling laugh broke the silence, growing louder and more menacing with each second.

"Interesting… interesting!" The voice was deep, laced with amusement and malice. "You've got good instincts, kid. Better than I expected." 

Kai didn't answer. His revolver dangled loosely in his palm, and he maintained the same expressionless look, as if death itself didn't worry him. 

The sound of the intruder's harsh, mocking laugh reverberated off the walls. "You're at ease." The voice continued, "I'll give you that," as it gently circled him while keeping the blade near his throat. "But I'm wondering why, as soon as you realised I was here, you didn't just try to kill me?" Kai's tone remained steady as he cocked his head slightly. "Because I'd rather not."

This time, the laughter was louder. "Really? That appeals to me." Behind him, the shadow moved closer, threatening like a wolf. 

"You know," the stranger added ominously, "I considered selling you when I spotted you. You have a pale face? In certain markets, you could demand a high price."

Kai's demeanour remained unchanging, his vacant eyes focused on what lay ahead. The voice went on, ruthless and savvy, "but those unsightly marks on your skin will make it impossible, adding that it could be more profitable to hack you up. Humans always require new organs, such as kidneys, lungs, and hearts."

Kai did not respond, but the words lingered in the air like poison. "But there's a place where someone like you might be even more valuable," the intruder said

At last, Kai shifted, his chilly gaze locking with the dark figure's image in the mirror. "Finished speaking." 

The intruder gave a gloomy laugh. "Spine. That's nice. However, don't assume that my patience is a sign of hesitancy." Behind him, there was too much movement to follow. 

Something heavy hit Kai, causing pain to explode at the back of his head. In an instant, the room tilted and spun, blurring his vision. The distorted image in the mirror became blurry. His owing reflection was the last thing he saw before the darkness swept him away. Then nothing. 

—---

[A/N : Did you like the twist? If you liked, the review the story. I need more readers.]