For hundreds of years, there has been a legend that after sunset, a terrifying creature roams the world—these creatures are called "demons." Demons feed on humans, they are immortal and cannot be killed no matter the lethal wounds they receive. Even if they are chopped into pieces, they will still survive. The only thing that can truly destroy a demon is the sunlight of the day.
Where there are demons, there have also naturally been humans who took it upon themselves to slay these demons. These swordsmen gathered together over centuries to form an organization called the Demon Slayer Corps. They are not recognized by the government, but even today they still hunt demons and protect the peace of the world, making demons tremble with fear.
The Demon Slayer Corps wields a powerful weapon—Nichirin Blades. These swords are forged from a mysterious material that seems to carry the power of the sun. When a swordsman uses a Nichirin Blade to sever a demon's head, even the seemingly immortal demon turns to ash on the spot.
From Karasuma, Shinichi had learned a great deal, including about the current state of the world. He also learned an important piece of information: all demons seem to originate from one person—or rather, from that person's blood. It is that person's blood that has created the many demons of today. As for who that person was, Karasuma wouldn't dare say his name.
But Shinichi had his suspicions. He thought of those crimson eyes from that night—the man named Muzan...
...
Run! Run!
In the dark forest, a figure fled desperately, stumbling through the underbrush. In the moonlight, one could see that the fleeing figure had several sharp horns on its forehead and razor-sharp fangs—a demon, without a doubt.
But what could possibly be behind it? What was terrifying enough to make an almost indestructible demon flee in fear like this?
"What kind of monster is this?! Too scary! Even though we're both demons, that bastard can actually kill other demons! I have to run! I have to get out of here before dawn!" the horned demon muttered in terror.
Boom!! An explosion suddenly erupted in front of the horned demon, startling it so badly that it fell to the ground. As it struggled to get up, a figure emerged from the smoke, radiating intense heat.
His exposed skin glowed red, and his black pupils were slit like a predator's. Sharp fangs peeked from between his lips, and his black claws gleamed ominously. In his right hand, he clutched a bloodied, mangled head, with a thin green vine-like tendril extending from his palm into the demon's skull.
"Blood Demon Art: Vitality Drain!"
Under the terrified gaze of the horned demon, the head in Shinichi's hand rapidly shriveled up, until he crushed it into dust and let the remnants scatter to the wind.
"M-Master, please, spare me! I—I swear I won't eat humans ever again. Please, have mercy on me!" The horned demon's body trembled as it desperately pleaded.
Woof!! In the blink of an eye, a black streak lunged at the demon from behind. "Aagh!!!" The horned demon howled in agony as something clamped onto its back, tearing into it.
A small black shadow had latched onto the demon's back—Enji, the demonized Shiba Inu, was biting furiously at the demon's spine with his sharp teeth.
...
Crunch! With a stomp from Shinichi, the withered demon turned to ashes. The redness faded from Shinichi's skin, and the vine retracted into his palm.
"The fifth one," Shinichi silently counted in his mind. Over a month had passed since he had turned into a demon, and during this time, five demons had fallen to him and Enji.
Woof, woof! Enji, his mouth still stained with blood, ran around Shinichi's feet, tongue out, clearly proud of himself. Perhaps because Enji's demonization stemmed from Shinichi's blood, a mysterious bond had been established between them since that time.
Shinichi could sense Enji's thoughts and emotions. Of course, Enji was still a Shiba Inu, so Shinichi could only perceive simple emotions like "happy," "master," "hungry," "bored," and "teeth itchy." But even so, their teamwork was seamless, allowing them to easily hunt five demons.
Shinichi lit a small campfire, roasting the rabbit Enji had caught. Staring at the dripping fat over the flames, Shinichi's mind drifted. The roasted rabbit wasn't for him—since becoming a demon, Shinichi could no longer eat any food or even drink water. Only Enji remained unaffected, wagging his tail as he circled around the fragrant rabbit.
Enji's situation was unique. Rather than saying he became a demon dog, it would be more accurate to say that Enji was a Shiba Inu imbued with demon abilities. It seemed that Shinichi's demon blood merely attached itself to Enji, only activating during combat. Thus, Enji could still eat normally and walk in sunlight. Just these two things alone made Shinichi feel envious.
With the Blood Demon Art—Vitality Drain, Shinichi could survive by absorbing energy from other demons rather than needing to eat. But over the past month, Shinichi found himself increasingly unsure of his own identity, occasionally feeling lost. Was he still human, or was he fully a demon now?
While Shinichi stared blankly into the fire, Enji had already devoured the entire roasted rabbit and was now rolling around on Shinichi's lap, demanding playtime.
"One step at a time," Shinichi sighed inwardly, stroking Enji's plump belly.
...
The sun rose, its warmth awakening the earth and the villagers of Shiroi Village. This was an ordinary mountain village at the foot of Shiroi Mountain. The dozens of families living here depended on the mountain for their livelihoods. The mountain was named Shiroi because, long ago, it housed a famous white well. The well water was said to be pure and sweet, and tea brewed with it was exquisite. During the Heian period, it was even favored by the local daimyo. However, the white well had dried up centuries ago, and its legend remained only as a story told by the village elders.
"Hey, Yamada, are you heading up the mountain today?"
"Yeah, I have to. My family's running out of food. If I don't, my wife and kids will starve."
"But there are mountain demons up there—Hayakawa, Maeda, Matsui... none of them came back from the mountain. And Hirone, the only one who escaped, lost his mind. He keeps screaming about seeing demons."
"What else can I do? The police are too scared to go up there. I have no choice!"
Near the village entrance, two men dressed as woodcutters spoke with furrowed brows. As woodcutters, not being able to go up the mountain meant losing their livelihoods. Shiroi Mountain had always been rumored to have mountain demons, but recently, more than a dozen villagers had gone up and never returned. The older folks all said it was the work of demons.
At that moment, the two worried woodcutters noticed a group of young men from the village gathering, walking towards them with various weapons—hatchets, bows, arrows, throwing knives, and even a long naginata.
Sensing trouble, Yamada quickly stepped forward to block their path, shouting at the young man in the lead, "Jiro! What are you all planning to do?"
The young man, Jiro, responded proudly, "Mr. Yamada, we've all heard the stories of demons on the mountain. It's just something the old folks say to scare kids. Whatever's attacking people up there is probably just wild animals. We're prepared, and today we're going to eliminate this threat for the village! Don't worry, Mr. Yamada, soon everyone will be able to go up the mountain safely."
Yamada looked at Jiro's youthful, naive face, both angry and anxious. He scolded, "Nonsense! It doesn't matter if it's a demon or a wild animal, it's not something you brats can handle! Go back home! Don't meddle in things that are for adults to take care of!"
Amidst the commotion, no one noticed the small Shiba Inu wagging its tail near the village path, its fluffy ears perked up, listening intently.
In the dark cave, Shinichi opened his eyes, processing the information that Enji had heard. "Shiroi Mountain, a mountain demon? Hmm..."
Shinichi pondered, weighing the truth of this information. Over the past month, the demons he had hunted had mostly been discovered through overheard rumors like this.
But Japan had always had its share of ghost stories and legends, so most of the rumors Shinichi had heard about demons wreaking havoc were inaccurate. Would this one be false as well? On Shiroi Mountain, was it truly a demon causing harm, or just wild animals?